diff --git a/testsuite/00-hello_test.py b/testsuite/00-hello_test.py
index 9077ab97..cdc15379 100644
--- a/testsuite/00-hello_test.py
+++ b/testsuite/00-hello_test.py
@@ -9,12 +9,12 @@ import os
 
 from rsyncfns import (
     FROMDIR, RSYNC, RSYNC_PEER, SRCDIR, TODIR,
-    checkit, run_rsync, test_fail,
+    checkit, run_rsync, test_fail, rsync_path_arg, rsh_cmd,
 )
 
 
 # Set RSYNC_RSH so rsync picks up lsh.sh for the "lh:" hosts below.
-os.environ['RSYNC_RSH'] = str(SRCDIR / 'support' / 'lsh.sh')
+os.environ['RSYNC_RSH'] = rsh_cmd()
 
 # Basic help dumps must not crash.
 if run_rsync('--version', check=False).returncode != 0:
@@ -39,7 +39,7 @@ def append_line(line: str) -> None:
 
 def copy_weird(args: list, src_host: str, dst_host: str) -> None:
     checkit(
-        [*args, f'--rsync-path={RSYNC_PEER}',
+        [*args, f'--rsync-path={rsync_path_arg()}',
          f'{src_host}{weird_dir}/',
          f'{dst_host}{TODIR / weird_name}'],
         FROMDIR, TODIR,
@@ -70,7 +70,7 @@ print('test6')
 saved = os.getcwd()
 os.chdir(FROMDIR)
 try:
-    run_rsync('-ai', '--old-args', f'--rsync-path={RSYNC_PEER}',
+    run_rsync('-ai', '--old-args', f'--rsync-path={rsync_path_arg()}',
               'lh:one two', f'{TODIR}/')
 finally:
     os.chdir(saved)
@@ -91,7 +91,7 @@ from rsyncfns import rsync_argv
 os.chdir(FROMDIR)
 try:
     subprocess.run(
-        rsync_argv('-ai', f'--rsync-path={RSYNC_PEER}',
+        rsync_argv('-ai', f'--rsync-path={rsync_path_arg()}',
                    'lh:one two', f'{TODIR}/'),
         env=env, check=True,
     )
diff --git a/testsuite/alt-dest_test.py b/testsuite/alt-dest_test.py
index d5bb37b2..19bce222 100644
--- a/testsuite/alt-dest_test.py
+++ b/testsuite/alt-dest_test.py
@@ -12,7 +12,7 @@ import time
 
 from rsyncfns import (
     CHKDIR, FROMDIR, RSYNC, RSYNC_PEER, SCRATCHDIR, SRCDIR, TMPDIR, TODIR,
-    checkit, hands_setup, rmtree, run_rsync, test_fail,
+    checkit, hands_setup, rmtree, run_rsync, test_fail, rsync_path_arg, rsh_cmd,
 )
 
 
@@ -20,7 +20,7 @@ alt1dir = TMPDIR / 'alt1'
 alt2dir = TMPDIR / 'alt2'
 alt3dir = TMPDIR / 'alt3'
 
-SSH = str(SRCDIR / 'support' / 'lsh.sh')
+SSH = rsh_cmd()
 
 hands_setup()
 
@@ -73,7 +73,7 @@ for maybe_inplace in ([], ['--inplace']):
     for srchost in ('', 'localhost:'):
         desthost = 'localhost:' if not srchost else ''
         rmtree(TODIR)
-        checkit(['-ave', SSH, f'--rsync-path={RSYNC_PEER}', *maybe_inplace,
+        checkit(['-ave', SSH, f'--rsync-path={rsync_path_arg()}', *maybe_inplace,
                  f'--copy-dest={alt3dir}',
                  f'{srchost}{FROMDIR}/', f'{desthost}{TODIR}/'],
                 FROMDIR, TODIR)
diff --git a/testsuite/basis-xname-traversal_test.py b/testsuite/basis-xname-traversal_test.py
index a51e6efe..de004c0e 100644
--- a/testsuite/basis-xname-traversal_test.py
+++ b/testsuite/basis-xname-traversal_test.py
@@ -35,6 +35,7 @@
 #   - neither flag -> the injection never took effect -> FAIL (vacuous)
 
 import os
+import shlex
 import subprocess
 import time
 from pathlib import Path
@@ -154,7 +155,7 @@ def attempt():
         conf = write_daemon_conf(
             [('m', {'path': str(serversrc), 'read only': 'yes', 'use chroot': 'no'})],
             name='mal-xname-rsyncd.conf')
-        os.environ['RSYNC_CONNECT_PROG'] = f'{mal_rsync} --config={conf} --daemon'
+        os.environ['RSYNC_CONNECT_PROG'] = f'{shlex.quote(str(mal_rsync))} --config={shlex.quote(str(conf))} --daemon'
         os.environ['RSYNC_MAL_XNAME'] = '../secret'  # from basis_dir[0] == linkdest
         proc = subprocess.run(
             rsync_argv('-a', f'--link-dest={linkdest}',
diff --git a/testsuite/daemon_test.py b/testsuite/daemon_test.py
index 525c7c70..3b1adda4 100644
--- a/testsuite/daemon_test.py
+++ b/testsuite/daemon_test.py
@@ -16,14 +16,14 @@ import subprocess
 from rsyncfns import (
     CHKFILE, FROMDIR, OUTFILE, RSYNC, RSYNC_PEER, SCRATCHDIR, SRCDIR, TODIR,
     build_rsyncd_conf, get_rootuid, get_testuid, makepath,
-    rsync_argv, run_rsync, start_test_daemon, test_fail,
+    rsync_argv, run_rsync, start_test_daemon, test_fail, rsh_cmd,
 )
 
 
 DAEMON_PORT = 12877
 
 
-SSH = f"{SRCDIR / 'support' / 'lsh.sh'} --no-cd"
+SSH = rsh_cmd(None, '--no-cd')
 
 
 def listed_paths(text: str) -> set:
diff --git a/testsuite/exclude_test.py b/testsuite/exclude_test.py
index bd528f61..a35901c2 100644
--- a/testsuite/exclude_test.py
+++ b/testsuite/exclude_test.py
@@ -17,7 +17,7 @@ import sys
 from rsyncfns import (
     CHKDIR, FROMDIR, RSYNC, RSYNC_PEER, SCRATCHDIR, SRCDIR, TMPDIR, TODIR,
     all_plus, allspace, dots,
-    checkdiff, checkit, makepath, rsync_argv, run_rsync, test_fail,
+    checkdiff, checkit, makepath, rsync_argv, run_rsync, test_fail, rsync_path_arg, rsh_cmd,
 )
 
 
@@ -25,8 +25,8 @@ os.environ['CVSIGNORE'] = '*.junk'
 
 script_name = os.path.basename(sys.argv[0] if sys.argv[0] else __file__)
 if 'lsh' in script_name:
-    os.environ['RSYNC_RSH'] = str(SRCDIR / 'support' / 'lsh.sh')
-    rpath = [f'--rsync-path={RSYNC_PEER}']
+    os.environ['RSYNC_RSH'] = rsh_cmd()
+    rpath = [f'--rsync-path={rsync_path_arg()}']
     host = 'lh:'
 else:
     rpath = []
@@ -116,7 +116,7 @@ excl.write_text(
 # --- main checks ------------------------------------------------------------
 
 # Start with a check of --prune-empty-dirs.
-run_rsync('-av', f'--rsync-path={RSYNC_PEER}',
+run_rsync('-av', f'--rsync-path={rsync_path_arg()}',
           '-f', '-_foo/too/', '-f', '-_foo/down/',
           '-f', '-_foo/and/', '-f', '-_new/',
           f'{host}{FROMDIR}/', f'{CHKDIR}/')
@@ -162,7 +162,7 @@ for f in (CHKDIR / 'bar' / 'down' / 'to' / 'foo').glob('file[235-9]'):
 (up2 / 'dst-newness').touch()
 
 # Un-tweak the directory times in our first (weak) exclude test.
-run_rsync('-av', f'--rsync-path={RSYNC_PEER}',
+run_rsync('-av', f'--rsync-path={rsync_path_arg()}',
           '--existing', '--include=*/', '--exclude=*',
           f'{host}{FROMDIR}/', f'{CHKDIR}/')
 
@@ -181,7 +181,7 @@ for f in (CHKDIR / 'bar' / 'down' / 'to' / 'foo').glob('*.junk'):
 (CHKDIR / 'bar' / 'down' / 'to' / 'home-cvs-exclude').unlink()
 (CHKDIR / 'mid' / 'one-in-one-out').unlink()
 
-run_rsync('-av', f'--rsync-path={RSYNC_PEER}',
+run_rsync('-av', f'--rsync-path={rsync_path_arg()}',
           '--existing', '--filter=exclude,! */',
           f'{host}{FROMDIR}/', f'{CHKDIR}/')
 
@@ -205,7 +205,7 @@ from rsyncfns import cp_touch
 cp_touch(FROMDIR / 'bar' / 'down' / 'to' / 'foo' / 'to',
          CHKDIR / 'bar' / 'down' / 'to' / 'foo')
 
-run_rsync('-av', f'--rsync-path={RSYNC_PEER}',
+run_rsync('-av', f'--rsync-path={rsync_path_arg()}',
           '--existing', '-f', 'show .filt*', '-f', 'hide,! */', '--del',
           f'{host}{FROMDIR}/', f'{TODIR}/')
 
@@ -213,7 +213,7 @@ run_rsync('-av', f'--rsync-path={RSYNC_PEER}',
 cp_touch(TODIR / 'bar' / 'down' / 'to' / 'bar' / 'baz' / 'nodel.deep',
          CHKDIR / 'bar' / 'down' / 'to' / 'bar' / 'baz')
 
-run_rsync('-av', f'--rsync-path={RSYNC_PEER}',
+run_rsync('-av', f'--rsync-path={rsync_path_arg()}',
           '--existing', '--filter=-! */',
           f'{host}{FROMDIR}/', f'{CHKDIR}/')
 
@@ -255,7 +255,7 @@ verify_dirs(CHKDIR, TODIR, label="dir-merge + merge-from-stdin")
 (CHKDIR / 'bar' / 'down' / 'to' / 'bar' / '.filt2').unlink()
 (CHKDIR / 'mid' / '.filt').unlink()
 
-run_rsync('-av', f'--rsync-path={RSYNC_PEER}',
+run_rsync('-av', f'--rsync-path={rsync_path_arg()}',
           '--existing', '--include=*/', '--exclude=*',
           f'{host}{FROMDIR}/', f'{CHKDIR}/')
 
@@ -275,15 +275,15 @@ verify_dirs(CHKDIR, TODIR, label="delete-before with merge")
     "+ file3\n*.bak\n"
 )
 
-run_rsync('-av', f'--rsync-path={RSYNC_PEER}',
+run_rsync('-av', f'--rsync-path={rsync_path_arg()}',
           '--del', f'{host}{FROMDIR}/', f'{CHKDIR}/')
 (CHKDIR / 'bar' / 'down' / 'to' / 'foo' / 'file1.bak').unlink()
 (CHKDIR / 'bar' / 'down' / 'to' / 'foo' / 'file3').unlink()
 (CHKDIR / 'bar' / 'down' / 'to' / 'foo' / '+ file3').unlink()
-run_rsync('-av', f'--rsync-path={RSYNC_PEER}',
+run_rsync('-av', f'--rsync-path={rsync_path_arg()}',
           '--existing', '--filter=-! */',
           f'{host}{FROMDIR}/', f'{CHKDIR}/')
-run_rsync('-av', f'--rsync-path={RSYNC_PEER}',
+run_rsync('-av', f'--rsync-path={rsync_path_arg()}',
           '--delete-excluded', '--exclude=*',
           f'{host}{FROMDIR}/', f'{TODIR}/')
 
@@ -293,7 +293,7 @@ checkit(['-avv', *rpath, '-f', 'dir-merge,-_.excl',
 
 # Combine with --relative.
 relative_opts = ['--relative', '--chmod=Du+w', '--copy-unsafe-links']
-run_rsync('-av', f'--rsync-path={RSYNC_PEER}', *relative_opts,
+run_rsync('-av', f'--rsync-path={rsync_path_arg()}', *relative_opts,
           f'{host}{FROMDIR}/foo', f'{CHKDIR}/')
 shutil.rmtree(str(CHKDIR) + str(FROMDIR) + '/foo/down', ignore_errors=True)
 run_rsync('-av', *relative_opts, '--existing', '--filter=-! */',
diff --git a/testsuite/files-from_test.py b/testsuite/files-from_test.py
index 0d10d2d5..faab43b9 100644
--- a/testsuite/files-from_test.py
+++ b/testsuite/files-from_test.py
@@ -7,11 +7,11 @@
 
 from rsyncfns import (
     CHKDIR, FROMDIR, RSYNC, RSYNC_PEER, SCRATCHDIR, SRCDIR, TODIR,
-    checkit, hands_setup, rmtree, run_rsync,
+    checkit, hands_setup, rmtree, run_rsync, rsync_path_arg, rsh_cmd,
 )
 
 
-SSH = str(SRCDIR / 'support' / 'lsh.sh')
+SSH = rsh_cmd()
 
 hands_setup()
 
@@ -44,7 +44,7 @@ for filehost in ('', 'localhost:'):
 
         rmtree(TODIR)
         checkit(
-            ['-avse', SSH, f'--rsync-path={RSYNC_PEER}',
+            ['-avse', SSH, f'--rsync-path={rsync_path_arg()}',
              f'--files-from={filehost}{filelist}',
              f'{srchost}{SCRATCHDIR}', f'{desthost}{TODIR}/'],
             CHKDIR, TODIR,
diff --git a/testsuite/hardlinks_test.py b/testsuite/hardlinks_test.py
index a578d63c..728264f0 100644
--- a/testsuite/hardlinks_test.py
+++ b/testsuite/hardlinks_test.py
@@ -13,11 +13,11 @@ import subprocess
 
 from rsyncfns import (
     CHKDIR, FROMDIR, OUTFILE, RSYNC, RSYNC_PEER, SRCDIR, TODIR,
-    checkit, makepath, rsync_argv, test_fail, test_skipped,
+    checkit, makepath, rsync_argv, test_fail, test_skipped, rsync_path_arg, rsh_cmd,
 )
 
 
-SSH = str(SRCDIR / 'support' / 'lsh.sh')
+SSH = rsh_cmd()
 
 FROMDIR.mkdir(parents=True, exist_ok=True)
 name1 = FROMDIR / 'name1'
@@ -64,7 +64,7 @@ for x in chars:
 os.link(name1, FROMDIR / 'subdir' / 'down' / 'deep' / 'new-file')
 (TODIR / 'text').unlink()
 
-checkit(['-aHivve', SSH, '--debug=HLINK5', f'--rsync-path={RSYNC_PEER}',
+checkit(['-aHivve', SSH, '--debug=HLINK5', f'--rsync-path={rsync_path_arg()}',
          f'{FROMDIR}/', f'localhost:{TODIR}/'], FROMDIR, TODIR)
 
 # --link-dest and --copy-dest should also keep hard-linked entries.
diff --git a/testsuite/malicious-sender-delete-scope_test.py b/testsuite/malicious-sender-delete-scope_test.py
index 3fb32463..34f10943 100644
--- a/testsuite/malicious-sender-delete-scope_test.py
+++ b/testsuite/malicious-sender-delete-scope_test.py
@@ -42,6 +42,7 @@
 #     diagnostic).
 
 import os
+import shlex
 import shutil
 import subprocess
 
@@ -126,7 +127,7 @@ conf = write_daemon_conf(
             'read only': 'yes',
             'use chroot': 'no'})],
     name='mal-rsyncd.conf')
-os.environ['RSYNC_CONNECT_PROG'] = f'{mal_rsync} --config={conf} --daemon'
+os.environ['RSYNC_CONNECT_PROG'] = f'{shlex.quote(str(mal_rsync))} --config={shlex.quote(str(conf))} --daemon'
 
 
 # -- The attack pull: -rR --delete from the malicious daemon -----------------
diff --git a/testsuite/remote-shell-newline-escaping_test.py b/testsuite/remote-shell-newline-escaping_test.py
index 3c339fc5..89b28147 100644
--- a/testsuite/remote-shell-newline-escaping_test.py
+++ b/testsuite/remote-shell-newline-escaping_test.py
@@ -9,7 +9,7 @@
 import os
 import subprocess
 
-from rsyncfns import SCRATCHDIR, SRCDIR, rmtree, rsync_argv, test_fail
+from rsyncfns import SCRATCHDIR, SRCDIR, rmtree, rsync_argv, test_fail, rsh_cmd
 
 base = SCRATCHDIR / 'remote-shell-newline'
 rmtree(base)
@@ -19,7 +19,7 @@ src.mkdir(parents=True)
 sentinel = base / 'pwned'
 
 env = os.environ.copy()
-env['RSYNC_RSH'] = f"{SRCDIR / 'support' / 'lsh.sh'} --no-cd"
+env['RSYNC_RSH'] = rsh_cmd(None, '--no-cd')
 dest = f"lh:{base}/dest\ntouch {sentinel}\n#"
 subprocess.run(rsync_argv('-a', f'{src}/', dest),
                stdout=subprocess.PIPE, stderr=subprocess.PIPE, text=True, env=env)
diff --git a/testsuite/rrsync-alt-dest-inband-pivot_test.py b/testsuite/rrsync-alt-dest-inband-pivot_test.py
index 3b6cefaa..ad60128d 100644
--- a/testsuite/rrsync-alt-dest-inband-pivot_test.py
+++ b/testsuite/rrsync-alt-dest-inband-pivot_test.py
@@ -10,6 +10,7 @@ out-of-tree content lands where it can be read back.
 """
 
 import os
+import shlex
 import signal
 import subprocess
 import sys
@@ -25,7 +26,8 @@ if '--shell' in sys.argv:
     os.execve(wrapper, [wrapper, '-wo', root], env)
 
 from rsyncfns import (RSYNC, SCRATCHDIR, makepath, patched_rrsync,
-                      proc_self_fd_pins, rmtree, rsync_argv)
+                      proc_self_fd_pins, rmtree, rsync_argv, rsync_path_arg,
+)
 
 T = 1234567890
 
@@ -59,10 +61,10 @@ os.utime(outside / 'f0', (T, T))
 # while rrsync hands its RSYNC to execlp() as a single executable name, so it
 # has to be wrapped before patched_rrsync() sees it.
 shim = base / 'rsync-shim'
-shim.write_text('#!/bin/sh\nexec ' + RSYNC + ' "$@"\n')
+shim.write_text('#!/bin/sh\nexec ' + rsync_path_arg(RSYNC) + ' "$@"\n')
 shim.chmod(0o755)
 wrapper = patched_rrsync(base, rsync_path=str(shim))
-rsh = f'{sys.executable} {os.path.abspath(__file__)} --shell'
+rsh = f'{shlex.quote(sys.executable)} {shlex.quote(os.path.abspath(__file__))} --shell'
 env = {**os.environ, 'RRSYNC_WRAPPER': str(wrapper), 'RRSYNC_ROOT': str(root)}
 
 got = subprocess.run(
diff --git a/testsuite/rrsync-backup-dir-inband-pivot_test.py b/testsuite/rrsync-backup-dir-inband-pivot_test.py
index e15d9d1d..3a2a15a4 100644
--- a/testsuite/rrsync-backup-dir-inband-pivot_test.py
+++ b/testsuite/rrsync-backup-dir-inband-pivot_test.py
@@ -2,6 +2,7 @@
 """rrsync must not let one transfer create and consume an option-path symlink."""
 
 import os
+import shlex
 import signal
 import subprocess
 import sys
@@ -18,7 +19,8 @@ if '--shell' in sys.argv:
     os.execve(wrapper, [wrapper, '-wo', root], env)
 
 from rsyncfns import (RSYNC, SCRATCHDIR, makepath, patched_rrsync,
-                      proc_self_fd_pins, rmtree, rsync_argv)
+                      proc_self_fd_pins, rmtree, rsync_argv, rsync_path_arg,
+)
 
 # Handing rsync an inode instead of a name needs the /proc/self/fd primitive.
 # Where it is missing there is no safe way to pass a peer-suppliable option
@@ -43,10 +45,10 @@ os.symlink('../outside', src / 'a')
 # while rrsync hands its RSYNC to execlp() as a single executable name, so it
 # has to be wrapped before patched_rrsync() sees it.
 shim = base / 'rsync-shim'
-shim.write_text('#!/bin/sh\nexec ' + RSYNC + ' "$@"\n')
+shim.write_text('#!/bin/sh\nexec ' + rsync_path_arg(RSYNC) + ' "$@"\n')
 shim.chmod(0o755)
 wrapper = patched_rrsync(base, rsync_path=str(shim))
-rsh = f'{sys.executable} {os.path.abspath(__file__)} --shell'
+rsh = f'{shlex.quote(sys.executable)} {shlex.quote(os.path.abspath(__file__))} --shell'
 env = {**os.environ, 'RRSYNC_WRAPPER': str(wrapper), 'RRSYNC_ROOT': str(root)}
 
 seed = subprocess.run(
diff --git a/testsuite/rrsync-files-from-stdin_test.py b/testsuite/rrsync-files-from-stdin_test.py
index 13696abf..24eabeae 100644
--- a/testsuite/rrsync-files-from-stdin_test.py
+++ b/testsuite/rrsync-files-from-stdin_test.py
@@ -25,7 +25,7 @@ import shlex
 import subprocess
 
 from rsyncfns import (
-    RSYNC, SCRATCHDIR, makepath, patched_rrsync, rmtree, rsync_argv, test_fail,
+    RSYNC, SCRATCHDIR, makepath, patched_rrsync, rmtree, rsync_argv, test_fail, rsync_path_arg,
 )
 
 DATA = 'FILES-FROM-CONTENT\n'
@@ -47,7 +47,7 @@ listfile.write_text('f1\nf2\n')
 # $RSYNC may carry a wrapper (valgrind, --protocol=N); rrsync wants a single
 # executable, so hand it a shim that re-expands the whole command line.
 shim = base / 'rsync-shim'
-shim.write_text('#!/bin/sh\nexec ' + RSYNC + ' "$@"\n')
+shim.write_text('#!/bin/sh\nexec ' + rsync_path_arg(RSYNC) + ' "$@"\n')
 shim.chmod(0o755)
 
 rrsync = patched_rrsync(base, rsync_path=str(shim))
diff --git a/testsuite/rrsync-no-overwrite-backup-collision_test.py b/testsuite/rrsync-no-overwrite-backup-collision_test.py
index 308e3e2d..c3009a8f 100644
--- a/testsuite/rrsync-no-overwrite-backup-collision_test.py
+++ b/testsuite/rrsync-no-overwrite-backup-collision_test.py
@@ -8,6 +8,7 @@ file can land on a protected name that the source itself also carries.
 """
 
 import os
+import shlex
 import signal
 import subprocess
 import sys
@@ -23,7 +24,7 @@ if '--shell' in sys.argv:
     flags = env.get('RRSYNC_FLAGS', '-wo -no-overwrite -no-lock').split()
     os.execve(wrapper, [wrapper, *flags, root], env)
 
-from rsyncfns import RSYNC, SCRATCHDIR, makepath, patched_rrsync, rmtree, rsync_argv
+from rsyncfns import RSYNC, SCRATCHDIR, makepath, patched_rrsync, rmtree, rsync_argv, rsync_path_arg
 
 base = SCRATCHDIR / 'rrsync-no-overwrite-backup-collision'
 rmtree(base)
@@ -46,10 +47,10 @@ plant(root)
 # while rrsync hands its RSYNC to execlp() as a single executable name, so it
 # has to be wrapped before patched_rrsync() sees it.
 shim = base / 'rsync-shim'
-shim.write_text('#!/bin/sh\nexec ' + RSYNC + ' "$@"\n')
+shim.write_text('#!/bin/sh\nexec ' + rsync_path_arg(RSYNC) + ' "$@"\n')
 shim.chmod(0o755)
 wrapper = patched_rrsync(base, rsync_path=str(shim))
-rsh = f'{sys.executable} {os.path.abspath(__file__)} --shell'
+rsh = f'{shlex.quote(sys.executable)} {shlex.quote(os.path.abspath(__file__))} --shell'
 env = {**os.environ, 'RRSYNC_WRAPPER': str(wrapper), 'RRSYNC_ROOT': str(root)}
 
 # The stock client sends -b inside the remote short-option bundle, so the
diff --git a/testsuite/rrsync-no-overwrite-delay-updates_test.py b/testsuite/rrsync-no-overwrite-delay-updates_test.py
index c2e681cf..0cd53f09 100644
--- a/testsuite/rrsync-no-overwrite-delay-updates_test.py
+++ b/testsuite/rrsync-no-overwrite-delay-updates_test.py
@@ -2,6 +2,7 @@
 """rrsync -no-overwrite must protect implicit delay-update partial files."""
 
 import os
+import shlex
 import signal
 import subprocess
 import sys
@@ -17,7 +18,7 @@ if '--shell' in sys.argv:
     flags = env.get('RRSYNC_FLAGS', '-wo -no-overwrite -no-lock').split()
     os.execve(wrapper, [wrapper, *flags, root], env)
 
-from rsyncfns import RSYNC, SCRATCHDIR, makepath, patched_rrsync, rmtree, rsync_argv
+from rsyncfns import RSYNC, SCRATCHDIR, makepath, patched_rrsync, rmtree, rsync_argv, rsync_path_arg
 
 base = SCRATCHDIR / 'rrsync-no-overwrite-delay-updates'
 rmtree(base)
@@ -32,10 +33,10 @@ protected.write_bytes(b'POLICY')
 # while rrsync hands its RSYNC to execlp() as a single executable name, so it
 # has to be wrapped before patched_rrsync() sees it.
 shim = base / 'rsync-shim'
-shim.write_text('#!/bin/sh\nexec ' + RSYNC + ' "$@"\n')
+shim.write_text('#!/bin/sh\nexec ' + rsync_path_arg(RSYNC) + ' "$@"\n')
 shim.chmod(0o755)
 wrapper = patched_rrsync(base, rsync_path=str(shim))
-rsh = f'{sys.executable} {os.path.abspath(__file__)} --shell'
+rsh = f'{shlex.quote(sys.executable)} {shlex.quote(os.path.abspath(__file__))} --shell'
 env = {**os.environ, 'RRSYNC_WRAPPER': str(wrapper), 'RRSYNC_ROOT': str(root)}
 got = subprocess.run(
     rsync_argv('-rI', '--delay-updates', '-e', rsh,
diff --git a/testsuite/rrsync-no-overwrite-logfile_test.py b/testsuite/rrsync-no-overwrite-logfile_test.py
index edfb4b05..89d6b6e3 100644
--- a/testsuite/rrsync-no-overwrite-logfile_test.py
+++ b/testsuite/rrsync-no-overwrite-logfile_test.py
@@ -2,6 +2,7 @@
 """rrsync -no-overwrite must not let the peer append to an existing file."""
 
 import os
+import shlex
 import signal
 import subprocess
 import sys
@@ -17,7 +18,7 @@ if '--shell' in sys.argv:
     flags = env.get('RRSYNC_FLAGS', '-wo -no-overwrite -no-lock').split()
     os.execve(wrapper, [wrapper, *flags, root], env)
 
-from rsyncfns import RSYNC, SCRATCHDIR, makepath, patched_rrsync, rmtree, rsync_argv
+from rsyncfns import RSYNC, SCRATCHDIR, makepath, patched_rrsync, rmtree, rsync_argv, rsync_path_arg
 
 base = SCRATCHDIR / 'rrsync-no-overwrite-logfile'
 rmtree(base)
@@ -32,10 +33,10 @@ protected.write_bytes(b'POLICY\n')
 # while rrsync hands its RSYNC to execlp() as a single executable name, so it
 # has to be wrapped before patched_rrsync() sees it.
 shim = base / 'rsync-shim'
-shim.write_text('#!/bin/sh\nexec ' + RSYNC + ' "$@"\n')
+shim.write_text('#!/bin/sh\nexec ' + rsync_path_arg(RSYNC) + ' "$@"\n')
 shim.chmod(0o755)
 wrapper = patched_rrsync(base, rsync_path=str(shim))
-rsh = f'{sys.executable} {os.path.abspath(__file__)} --shell'
+rsh = f'{shlex.quote(sys.executable)} {shlex.quote(os.path.abspath(__file__))} --shell'
 env = {**os.environ, 'RRSYNC_WRAPPER': str(wrapper), 'RRSYNC_ROOT': str(root)}
 got = subprocess.run(
     rsync_argv('-rI', '-M--log-file=protected',
diff --git a/testsuite/rrsync-no-overwrite-partial-dir_test.py b/testsuite/rrsync-no-overwrite-partial-dir_test.py
index fe5ae17f..5b5a15e4 100644
--- a/testsuite/rrsync-no-overwrite-partial-dir_test.py
+++ b/testsuite/rrsync-no-overwrite-partial-dir_test.py
@@ -2,6 +2,7 @@
 """rrsync -no-overwrite must protect existing partial-dir files too."""
 
 import os
+import shlex
 import signal
 import subprocess
 import sys
@@ -17,7 +18,7 @@ if '--shell' in sys.argv:
     flags = env.get('RRSYNC_FLAGS', '-wo -no-overwrite -no-lock').split()
     os.execve(wrapper, [wrapper, *flags, root], env)
 
-from rsyncfns import RSYNC, SCRATCHDIR, makepath, patched_rrsync, rmtree, rsync_argv
+from rsyncfns import RSYNC, SCRATCHDIR, makepath, patched_rrsync, rmtree, rsync_argv, rsync_path_arg
 
 base = SCRATCHDIR / 'rrsync-no-overwrite-partial-dir'
 rmtree(base)
@@ -32,10 +33,10 @@ protected.write_bytes(b'POLICY')
 # while rrsync hands its RSYNC to execlp() as a single executable name, so it
 # has to be wrapped before patched_rrsync() sees it.
 shim = base / 'rsync-shim'
-shim.write_text('#!/bin/sh\nexec ' + RSYNC + ' "$@"\n')
+shim.write_text('#!/bin/sh\nexec ' + rsync_path_arg(RSYNC) + ' "$@"\n')
 shim.chmod(0o755)
 wrapper = patched_rrsync(base, rsync_path=str(shim))
-rsh = f'{sys.executable} {os.path.abspath(__file__)} --shell'
+rsh = f'{shlex.quote(sys.executable)} {shlex.quote(os.path.abspath(__file__))} --shell'
 env = {**os.environ, 'RRSYNC_WRAPPER': str(wrapper), 'RRSYNC_ROOT': str(root)}
 got = subprocess.run(
     rsync_argv('-rI', '--partial', '--partial-dir=protected',
diff --git a/testsuite/rrsync-pull-arg-shapes_test.py b/testsuite/rrsync-pull-arg-shapes_test.py
index eff3ffc4..f359f70c 100644
--- a/testsuite/rrsync-pull-arg-shapes_test.py
+++ b/testsuite/rrsync-pull-arg-shapes_test.py
@@ -23,7 +23,7 @@ import subprocess
 
 from rsyncfns import (
     RSYNC, SCRATCHDIR, forced_protocol, makepath, patched_rrsync, rmtree,
-    rsync_argv, test_fail,
+    rsync_argv, test_fail, rsync_path_arg,
 )
 
 base = SCRATCHDIR / 'rrsync-arg-shapes'
@@ -53,7 +53,7 @@ xonly.mkdir()
 xonly.chmod(0o111)
 
 shim = base / 'rsync-shim'
-shim.write_text('#!/bin/sh\nexec ' + RSYNC + ' "$@"\n')
+shim.write_text('#!/bin/sh\nexec ' + rsync_path_arg(RSYNC) + ' "$@"\n')
 shim.chmod(0o755)
 
 rrsync = patched_rrsync(base, rsync_path=str(shim))
diff --git a/testsuite/rrsync-pull-delivers-content_test.py b/testsuite/rrsync-pull-delivers-content_test.py
index 668abdd2..4947a58f 100644
--- a/testsuite/rrsync-pull-delivers-content_test.py
+++ b/testsuite/rrsync-pull-delivers-content_test.py
@@ -28,7 +28,7 @@ import shlex
 import subprocess
 
 from rsyncfns import (
-    RSYNC, SCRATCHDIR, makepath, patched_rrsync, rmtree, rsync_argv, test_fail,
+    RSYNC, SCRATCHDIR, makepath, patched_rrsync, rmtree, rsync_argv, test_fail, rsync_path_arg,
 )
 
 PULL_DATA = 'REAL-FILE-CONTENT\n'
@@ -50,7 +50,7 @@ makepath(restricted / 'inbox')
 # $RSYNC may carry a wrapper (valgrind, --protocol=N); rrsync wants a single
 # executable, so hand it a shim that re-expands the whole command line.
 shim = base / 'rsync-shim'
-shim.write_text('#!/bin/sh\nexec ' + RSYNC + ' "$@"\n')
+shim.write_text('#!/bin/sh\nexec ' + rsync_path_arg(RSYNC) + ' "$@"\n')
 shim.chmod(0o755)
 
 rrsync = patched_rrsync(base, rsync_path=str(shim))
diff --git a/testsuite/rrsync-sender-leaf-flip_test.py b/testsuite/rrsync-sender-leaf-flip_test.py
index d53db605..45e80f8f 100644
--- a/testsuite/rrsync-sender-leaf-flip_test.py
+++ b/testsuite/rrsync-sender-leaf-flip_test.py
@@ -38,7 +38,7 @@ import time
 from rsyncfns import (
     RACE_TIMEOUT, RSYNC, SCRATCHDIR, makepath, patched_rrsync,
     proc_self_fd_pins, rmtree, rsync_argv, start_path_flipper, stop_flipper,
-    test_fail, test_skipped,
+    test_fail, test_skipped, rsync_path_arg,
 )
 
 if not proc_self_fd_pins():
@@ -58,7 +58,7 @@ makepath(restricted, outside / 'dir', dest)
 (outside / 'dir' / 'loot').write_text(MARKER + '\n')
 
 shim = base / 'rsync-shim'
-shim.write_text('#!/bin/sh\nexec ' + RSYNC + ' "$@"\n')
+shim.write_text('#!/bin/sh\nexec ' + rsync_path_arg(RSYNC) + ' "$@"\n')
 shim.chmod(0o755)
 
 rrsync = patched_rrsync(base, rsync_path=str(shim))
diff --git a/testsuite/rrsync-specials-denied_test.py b/testsuite/rrsync-specials-denied_test.py
index 2b40949c..60d83723 100644
--- a/testsuite/rrsync-specials-denied_test.py
+++ b/testsuite/rrsync-specials-denied_test.py
@@ -34,7 +34,7 @@ import subprocess
 
 from rsyncfns import (
     RSYNC, RSYNC_PREFIX, SCRATCHDIR, patched_rrsync, rmtree, rsync_argv,
-    test_fail, xattr_set, xattrs_supported,
+    test_fail, xattr_set, xattrs_supported, rsync_path_arg,
 )
 
 base = SCRATCHDIR / 'rrsync-specials'
@@ -113,7 +113,7 @@ served.mkdir()
 pushwrap = base / 'pushwrap'
 pushwrap.mkdir()
 shim = base / 'rsync-shim'
-shim.write_text('#!/bin/sh\nexec ' + RSYNC + ' "$@"\n')
+shim.write_text('#!/bin/sh\nexec ' + rsync_path_arg(RSYNC) + ' "$@"\n')
 shim.chmod(0o755)
 rrsync_push = patched_rrsync(pushwrap, rsync_path=str(shim))
 rsh = base / 'fake-rsh'
@@ -175,7 +175,7 @@ if xattrs_supported():
         devwrap = base / 'devwrap'
         devwrap.mkdir()
         devshim = base / 'rsync-shim-fake'
-        devshim.write_text('#!/bin/sh\nexec ' + RSYNC + ' --fake-super "$@"\n')
+        devshim.write_text('#!/bin/sh\nexec ' + rsync_path_arg(RSYNC) + ' --fake-super "$@"\n')
         devshim.chmod(0o755)
         rrsync_dev = patched_rrsync(devwrap, rsync_path=str(devshim))
         devrsh = base / 'fake-rsh-dev'
diff --git a/testsuite/rrsync-write-only-files-from_test.py b/testsuite/rrsync-write-only-files-from_test.py
index 41f4f8e4..3d24f99f 100644
--- a/testsuite/rrsync-write-only-files-from_test.py
+++ b/testsuite/rrsync-write-only-files-from_test.py
@@ -2,6 +2,7 @@
 """A forced rrsync -wo endpoint must not return a local --files-from file."""
 
 import os
+import shlex
 import signal
 import subprocess
 import sys
@@ -16,7 +17,7 @@ if '--shell' in sys.argv:
     wrapper, root = env['RRSYNC_WRAPPER'], env['RRSYNC_ROOT']
     os.execve(wrapper, [wrapper, '-wo', '-no-lock', root], env)
 
-from rsyncfns import RSYNC, SCRATCHDIR, makepath, patched_rrsync, rmtree, rsync_argv
+from rsyncfns import RSYNC, SCRATCHDIR, makepath, patched_rrsync, rmtree, rsync_argv, rsync_path_arg
 
 base = SCRATCHDIR / 'rrsync-write-only-files-from'
 rmtree(base)
@@ -30,10 +31,10 @@ secret_name = 'SERVER-ONLY-SECRET-NAME'
 # while rrsync hands its RSYNC to execlp() as a single executable name, so it
 # has to be wrapped before patched_rrsync() sees it.
 shim = base / 'rsync-shim'
-shim.write_text('#!/bin/sh\nexec ' + RSYNC + ' "$@"\n')
+shim.write_text('#!/bin/sh\nexec ' + rsync_path_arg(RSYNC) + ' "$@"\n')
 shim.chmod(0o755)
 wrapper = patched_rrsync(base, rsync_path=str(shim))
-rsh = f'{sys.executable} {os.path.abspath(__file__)} --shell'
+rsh = f'{shlex.quote(sys.executable)} {shlex.quote(os.path.abspath(__file__))} --shell'
 env = {**os.environ, 'RRSYNC_WRAPPER': str(wrapper), 'RRSYNC_ROOT': str(root)}
 got = subprocess.run(
     rsync_argv('-r', '--files-from=:protected-list',
diff --git a/testsuite/rsyncfns.py b/testsuite/rsyncfns.py
index ad532841..c7bdabe5 100644
--- a/testsuite/rsyncfns.py
+++ b/testsuite/rsyncfns.py
@@ -23,6 +23,7 @@ import filecmp
 import errno
 import os
 import platform
+import re
 import shlex
 import shutil
 import signal
@@ -95,6 +96,14 @@ def split_rsync_cmd(cmd: str) -> list:
     """
     if os.path.isfile(cmd):
         return [cmd]
+    # The path may be followed by options -- chown-fake and friends append
+    # ' --fake-super' to RSYNC -- so the whole string is no longer a filename.
+    # Take the longest leading run that names an existing file as the program
+    # and split only what follows.
+    for m in reversed(list(re.finditer(r'\s+', cmd))):
+        head = cmd[:m.start()]
+        if os.path.isfile(head):
+            return [head] + shlex.split(cmd[m.start():])
     return shlex.split(cmd)
 
 
@@ -658,7 +667,10 @@ def start_test_daemon(conf_path, port: int, rsync_cmd: str = None) -> str:
         port = claim_free_port(port)
         start_rsyncd(conf_path, port, daemon_cmd)
         return f'rsync://localhost:{port}/'
-    os.environ['RSYNC_CONNECT_PROG'] = f'{daemon_cmd} --config={conf_path} --daemon'
+    # RSYNC_CONNECT_PROG is run by a shell, so every word has to survive
+    # re-parsing: a build path with a space would otherwise exec its prefix.
+    os.environ['RSYNC_CONNECT_PROG'] = (
+        f'{rsync_path_arg(daemon_cmd)} --config={shlex.quote(str(conf_path))} --daemon')
     return 'rsync://localhost/'
 
 
@@ -677,7 +689,7 @@ def require_asan(reason: str, which: str = None) -> 'None':
     pass RSYNC to check the client side. Detection runs the binary with
     ASAN_OPTIONS=help=1, which makes an instrumented binary print the ASan
     flag help banner to stderr."""
-    cmd = shlex.split(which or RSYNC_PEER)
+    cmd = split_rsync_cmd(which or RSYNC_PEER)
     try:
         r = subprocess.run(cmd + ['--version'],
                            env={**os.environ, 'ASAN_OPTIONS': 'help=1'},
@@ -690,6 +702,30 @@ def require_asan(reason: str, which: str = None) -> 'None':
         test_skipped(reason)
 
 
+def rsh_cmd(cmd: str = None, *opts: str) -> str:
+    """Build an RSYNC_RSH / --rsh value, quoted for rsync's own tokenizer.
+
+    rsync splits this string on spaces itself -- honouring ' and ", see do_cmd()
+    in main.c -- so a remote-shell path containing a space must be quoted or
+    rsync execs only the first word.  The testsuite's srcdir can contain one.
+    """
+    if cmd is None:
+        cmd = str(SRCDIR / 'support' / 'lsh.sh')
+    return ' '.join([shlex.quote(cmd), *opts])
+
+
+def rsync_path_arg(cmd: str = None) -> str:
+    """Value for --rsync-path, quoted for the shell that will re-parse it.
+
+    --rsync-path is a command line run by the remote shell, not a filename, so
+    rsync hands it over unquoted and the far side word-splits it.  A build path
+    containing a space therefore needs quoting here, while a wrapper command
+    ('valgrind ... /build/rsync') must stay several words.  Splitting and
+    re-joining with shlex gives both: each word is quoted only if it needs it.
+    """
+    return shlex.join(split_rsync_cmd(RSYNC_PEER if cmd is None else cmd))
+
+
 def rsync_argv(*args: str) -> list:
     """Return the argv for invoking rsync with the given extra arguments.
 
diff --git a/testsuite/scanner-argv-bounds_test.py b/testsuite/scanner-argv-bounds_test.py
index 02682877..f2eeea17 100644
--- a/testsuite/scanner-argv-bounds_test.py
+++ b/testsuite/scanner-argv-bounds_test.py
@@ -7,10 +7,10 @@
 import os
 import subprocess
 from rsyncfns import (
-    FROMDIR, RSYNC_PEER, SRCDIR, SCRATCHDIR, makepath, rmtree, rsync_argv, test_fail,
+    FROMDIR, RSYNC_PEER, SRCDIR, SCRATCHDIR, makepath, rmtree, rsync_argv, test_fail, rsync_path_arg, rsh_cmd,
 )
 
-LSH = str(SRCDIR / 'support' / 'lsh.sh')
+LSH = rsh_cmd()
 os.environ['RSYNC_RSH'] = LSH
 
 src = FROMDIR
@@ -27,7 +27,7 @@ def run(label, extra, local=False):
         argv = rsync_argv('-a', *extra, f'{src}/', f'{dest}/')
     else:
         argv = rsync_argv('-a', *extra, '-e', LSH,
-                          f'--rsync-path={RSYNC_PEER}', f'{src}/', f'localhost:{dest}/')
+                          f'--rsync-path={rsync_path_arg()}', f'{src}/', f'localhost:{dest}/')
     r = subprocess.run(argv, capture_output=True, text=True)
     if r.returncode < 0 or r.returncode >= 128:
         test_fail(f'{label}: rsync crashed (rc={r.returncode}): {r.stderr.strip()[:200]}')
diff --git a/testsuite/ssh-basic_test.py b/testsuite/ssh-basic_test.py
index eb658118..a02d55e9 100644
--- a/testsuite/ssh-basic_test.py
+++ b/testsuite/ssh-basic_test.py
@@ -12,11 +12,11 @@ import subprocess
 
 from rsyncfns import (
     FROMDIR, SRCDIR, TODIR,
-    checkit, hands_setup, runtest, test_skipped,
+    checkit, hands_setup, runtest, test_skipped, rsync_path_arg, rsh_cmd,
 )
 
 
-SSH = str(SRCDIR / 'support' / 'lsh.sh')
+SSH = rsh_cmd()
 
 # Allow opting into real ssh via the shconfig variable, like the shell test.
 if os.environ.get('rsync_enable_ssh_tests') == 'yes':
@@ -42,13 +42,13 @@ from rsyncfns import RSYNC, RSYNC_PEER
 
 
 def _basic():
-    checkit(['-avH', '-e', SSH, f'--rsync-path={RSYNC_PEER}',
+    checkit(['-avH', '-e', SSH, f'--rsync-path={rsync_path_arg()}',
              f'{FROMDIR}/', f'localhost:{TODIR}'], FROMDIR, TODIR)
 
 
 def _delete_after_rename():
     shutil.move(str(TODIR / 'text'), str(TODIR / 'ThisShouldGo'))
-    checkit(['--delete', '-avH', '-e', SSH, f'--rsync-path={RSYNC_PEER}',
+    checkit(['--delete', '-avH', '-e', SSH, f'--rsync-path={rsync_path_arg()}',
              f'{FROMDIR}/', f'localhost:{TODIR}'], FROMDIR, TODIR)
 
 
diff --git a/testsuite/symlink-dirlink-basis_test.py b/testsuite/symlink-dirlink-basis_test.py
index 9785a290..ffe368e2 100644
--- a/testsuite/symlink-dirlink-basis_test.py
+++ b/testsuite/symlink-dirlink-basis_test.py
@@ -19,7 +19,7 @@ import time
 
 from rsyncfns import (
     RSYNC, SCRATCHDIR, RSYNC_PEER, SRCDIR, TMPDIR,
-    make_data_file, rsync_argv, test_fail,
+    make_data_file, rsync_argv, test_fail, rsync_path_arg, rsh_cmd,
 )
 
 
@@ -28,7 +28,7 @@ from rsyncfns import (
 # target off held dirfds (issue #715), so this transfer through a dir-symlinked
 # basis succeeds uniformly.
 
-os.environ['RSYNC_RSH'] = str(SRCDIR / 'support' / 'lsh.sh')
+os.environ['RSYNC_RSH'] = rsh_cmd()
 # HOME -> SCRATCHDIR is set up by rsyncfns import.
 
 srcbase = TMPDIR / 'src_files'  # avoid clash with the runner's $scratchdir/src symlink
@@ -50,7 +50,7 @@ def push(*args, label: str) -> None:
     os.chdir(srcbase)
     try:
         proc = subprocess.run(
-            rsync_argv(f'--rsync-path={RSYNC_PEER}', *args),
+            rsync_argv(f'--rsync-path={rsync_path_arg()}', *args),
             stdout=subprocess.PIPE, stderr=subprocess.STDOUT, text=True,
         )
         print(proc.stdout, end='')
diff --git a/testsuite/variety-symlink-traversal_test.py b/testsuite/variety-symlink-traversal_test.py
index 89762d3a..9d37b3d4 100644
--- a/testsuite/variety-symlink-traversal_test.py
+++ b/testsuite/variety-symlink-traversal_test.py
@@ -26,10 +26,10 @@ from rsyncfns import (
     RSYNC, RSYNC_PEER, SRCDIR, SCRATCHDIR,
     make_variety_tree, compare_trees, rmtree,
     xattrs_supported, acls_supported, devices_supported, owners_supported,
-    test_skipped, test_fail, split_rsync_cmd,
+    test_skipped, test_fail, split_rsync_cmd, rsh_cmd,
 )
 
-SSH = str(SRCDIR / 'support' / 'lsh.sh')
+SSH = rsh_cmd()
 WITH_X = xattrs_supported()
 WITH_A = acls_supported()
 
diff --git a/testsuite/variety_test.py b/testsuite/variety_test.py
index bff73972..dfea53a3 100644
--- a/testsuite/variety_test.py
+++ b/testsuite/variety_test.py
@@ -34,10 +34,10 @@ from rsyncfns import (
     make_variety_tree, compare_trees, rmtree,
     xattrs_supported, acls_supported, devices_supported, owners_supported,
     write_daemon_conf, start_test_daemon,
-    test_fail, split_rsync_cmd,
+    test_fail, split_rsync_cmd, rsh_cmd,
 )
 
-SSH = str(SRCDIR / 'support' / 'lsh.sh')
+SSH = rsh_cmd()
 DAEMON_PORT_OLD = 12931
 DAEMON_PORT_NEW = 12932