diff --git a/meshtastic/tests/conftest.py b/meshtastic/tests/conftest.py
index d31fa31..596f4b1 100644
--- a/meshtastic/tests/conftest.py
+++ b/meshtastic/tests/conftest.py
@@ -15,6 +15,7 @@ from .firmware_harness import (
     find_meshtasticd,
     is_compatible_host,
 )
+from .fw_helpers import set_region
 
 # Use a different base port for the single-node fixture so it doesn't
 # conflict with the multi-node mesh fixture.
@@ -41,11 +42,14 @@ def firmware_node():
     tests be order-independent.
 
     Yields the SimNode instance.  The node is booted with a fresh erased
-    config and listens on localhost at its TCP port.
+    config and listens on localhost at its TCP port.  Region is set to US
+    so modem-preset tests work against firmware >= 2.8, which clamps
+    presets to the legal set for the current region.
     """
     _skip_firmware_if_unavailable()
     mesh = SimMesh(n_nodes=1, base_port=SINGLE_NODE_BASE_PORT)
     mesh.start()
+    set_region(mesh.get_node(0).port, "US")
     yield mesh.get_node(0)
     mesh.stop()
 
@@ -55,11 +59,24 @@ def firmware_mesh():
     """A 3-node chain (A-B-C) meshtasticd sim mesh for smokemesh tests.
 
     Yields the SimMesh instance.  Nodes are connected and the SIMULATOR_APP
-    packet bridge is running.  Node DB convergence is awaited.
+    packet bridge is running.  Region is set to US for firmware >= 2.8
+    compatibility, interfaces are reconnected after the region change, and
+    node DB convergence is awaited.
     """
     _skip_firmware_if_unavailable()
     mesh = SimMesh(n_nodes=3, topology=CHAIN_TOPOLOGY)
     mesh.start()
+    for node in mesh.nodes:
+        set_region(node.port, "US")
+    # The region commit restarts each node's TCP listener, so reconnect the
+    # harness interfaces before waiting for convergence.
+    for node in mesh.nodes:
+        if node.iface is not None:
+            try:
+                node.iface.close()
+            except Exception:  # pylint: disable=broad-except
+                pass
+        node.connect()
     mesh.wait_for_convergence(timeout=30)
     yield mesh
     mesh.stop()
diff --git a/meshtastic/tests/fw_helpers.py b/meshtastic/tests/fw_helpers.py
index f570f09..2bc2988 100644
--- a/meshtastic/tests/fw_helpers.py
+++ b/meshtastic/tests/fw_helpers.py
@@ -31,6 +31,11 @@ logger = logging.getLogger(__name__)
 # simulator happy when many short-lived connections are happening.
 PAUSE_AFTER_CLI = 0.2
 
+# Pause after changing the LoRa region. The firmware may restart the TCP
+# listener while committing the new radio config, so give it time to settle
+# before the next CLI call or harness reconnect.
+PAUSE_AFTER_REGION_CHANGE = 2.0
+
 
 # ---------------------------------------------------------------------------
 # CLI invocation
@@ -325,6 +330,19 @@ def subscribe_positions(iface: TCPInterface) -> PacketCollector:
     return _subscribe_topic(iface, "meshtastic.receive.position")
 
 
+def set_region(port: int, region: str = "US") -> None:
+    """Set the LoRa region on a sim node via the CLI.
+
+    The node briefly restarts its TCP listener while committing the radio
+    config; ``run_cli()`` handles the reconnect retry, and we sleep long
+    enough for the new region to take effect before callers continue.
+    """
+    rc, out = run_cli(port, "--set", "lora.region", region)
+    if rc != 0:
+        raise RuntimeError(f"Failed to set lora.region={region}: {out}")
+    time.sleep(PAUSE_AFTER_REGION_CHANGE)
+
+
 def unsubscribe_all(topic: str) -> None:
     """Drop every handler currently registered on *topic*.
 
@@ -339,12 +357,14 @@ def unsubscribe_all(topic: str) -> None:
 
 __all__ = [
     "PAUSE_AFTER_CLI",
+    "PAUSE_AFTER_REGION_CHANGE",
     "PacketCollector",
     "RECEIVE_TIMEOUT",
     "cli_then_verify",
     "connect_iface",
     "resolve_cli",
     "run_cli",
+    "set_region",
     "subscribe_positions",
     "subscribe_telemetries",
     "subscribe_texts",