diff --git a/generator.c b/generator.c
index b80eb2e3..38f5ad33 100644
--- a/generator.c
+++ b/generator.c
@@ -2146,6 +2146,8 @@ void check_for_finished_files(int itemizing, enum logcode code, int check_redo)
 			if (send_failed)
 				ndx = get_hlink_num();
 			flist = flist_for_ndx(ndx, "check_for_finished_files.1");
+			if (ndx < flist->ndx_start)
+				exit_cleanup(RERR_PROTOCOL);
 			file = flist->files[ndx - flist->ndx_start];
 			assert(file->flags & FLAG_HLINKED);
 			if (send_failed)
@@ -2174,6 +2176,8 @@ void check_for_finished_files(int itemizing, enum logcode code, int check_redo)
 
 			flist = cur_flist;
 			cur_flist = flist_for_ndx(ndx, "check_for_finished_files.2");
+			if (ndx < cur_flist->ndx_start)
+				exit_cleanup(RERR_PROTOCOL);
 
 			file = cur_flist->files[ndx - cur_flist->ndx_start];
 			if (solo_file)
diff --git a/io.c b/io.c
index 8d1cf7f2..2d94c1f4 100644
--- a/io.c
+++ b/io.c
@@ -1090,6 +1090,9 @@ static void got_flist_entry_status(enum festatus status, int ndx)
 {
 	struct file_list *flist = flist_for_ndx(ndx, "got_flist_entry_status");
 
+	if (ndx < flist->ndx_start)
+		exit_cleanup(RERR_PROTOCOL);
+
 	if (remove_source_files) {
 		active_filecnt--;
 		active_bytecnt -= F_LENGTH(flist->files[ndx - flist->ndx_start]);
diff --git a/receiver.c b/receiver.c
index 63e5cedb..0a993e0f 100644
--- a/receiver.c
+++ b/receiver.c
@@ -467,7 +467,10 @@ static void handle_delayed_updates(char *local_name)
 static void no_batched_update(int ndx, BOOL is_redo)
 {
 	struct file_list *flist = flist_for_ndx(ndx, "no_batched_update");
-	struct file_struct *file = flist->files[ndx - flist->ndx_start];
+	struct file_struct *file;
+	if (ndx < flist->ndx_start)
+		exit_cleanup(RERR_PROTOCOL);
+	file = flist->files[ndx - flist->ndx_start];
 
 	rprintf(FERROR_XFER, "(No batched update for%s \"%s\")\n",
 		is_redo ? " resend of" : "", f_name(file, NULL));
@@ -604,6 +607,8 @@ int recv_files(int f_in, int f_out, char *local_name)
 
 		if (ndx - cur_flist->ndx_start >= 0)
 			file = cur_flist->files[ndx - cur_flist->ndx_start];
+		else if (cur_flist->parent_ndx < 0)
+			exit_cleanup(RERR_PROTOCOL);
 		else
 			file = dir_flist->files[cur_flist->parent_ndx];
 		fname = local_name ? local_name : f_name(file, fbuf);
diff --git a/sender.c b/sender.c
index 99f431fe..033f87e5 100644
--- a/sender.c
+++ b/sender.c
@@ -140,6 +140,8 @@ void successful_send(int ndx)
 		return;
 
 	flist = flist_for_ndx(ndx, "successful_send");
+	if (ndx < flist->ndx_start)
+		exit_cleanup(RERR_PROTOCOL);
 	file = flist->files[ndx - flist->ndx_start];
 	if (!change_pathname(file, NULL, 0))
 		return;