diff --git a/esphome/components/sx126x/packet_interface/__init__.py b/esphome/components/sx126x/packet_interface/__init__.py
index 8af293d8a6a..117b2bc38e6 100644
--- a/esphome/components/sx126x/packet_interface/__init__.py
+++ b/esphome/components/sx126x/packet_interface/__init__.py
@@ -4,12 +4,15 @@ from esphome.components.packet_interface.radio_link import (
     radio_link_final_validate,
     radio_link_schema,
 )
+import esphome.config_validation as cv
 from esphome.types import ConfigType
 
 from .. import (
+    CONF_MODULATION,
     CONF_PAYLOAD_LENGTH,
     CONF_RX_START,
     CONF_SX126X_ID,
+    CONF_SYNC_VALUE,
     DOMAIN,
     SX126x,
     SX126xListener,
@@ -25,8 +28,21 @@ SX126xPacketInterface = sx126x_ns.class_(
 
 CONFIG_SCHEMA = radio_link_schema(SX126xPacketInterface, CONF_SX126X_ID, SX126x)
 
+
+def _check_fsk(config: ConfigType, radio: ConfigType) -> None:
+    """Without LoRa, the radio can tell that a packet is arriving only from its sync word, which listen before talk
+    needs.
+    """
+    if radio[CONF_MODULATION] != "LORA" and not radio[CONF_SYNC_VALUE]:
+        raise cv.Invalid(
+            f"Without LoRa modulation the radio needs a '{CONF_SYNC_VALUE}', so that the link can tell when a packet "
+            "is arriving and not send over it",
+            path=[CONF_SX126X_ID],
+        )
+
+
 FINAL_VALIDATE_SCHEMA = radio_link_final_validate(
-    CONF_SX126X_ID, CONF_PAYLOAD_LENGTH, CONF_RX_START
+    CONF_SX126X_ID, CONF_PAYLOAD_LENGTH, CONF_RX_START, _check_fsk
 )
 
 
diff --git a/tests/unit_tests/test_lora_packet_interface.py b/tests/unit_tests/test_lora_packet_interface.py
index 27140a42729..fc389430b91 100644
--- a/tests/unit_tests/test_lora_packet_interface.py
+++ b/tests/unit_tests/test_lora_packet_interface.py
@@ -90,7 +90,7 @@ class _FullConfig(dict):
         (
             sx126x_packet_interface,
             "sx126x",
-            {"payload_length": 10},
+            _lora(payload_length=10),
             {},
             "payload_length",
             {"payload_length": 0},
@@ -143,6 +143,14 @@ class _FullConfig(dict):
             "sync_value",
             {"preamble_detect": 2},
         ),
+        (
+            sx126x_packet_interface,
+            "sx126x",
+            {"modulation": "FSK", "payload_length": 0, "sync_value": []},
+            {},
+            "sync_value",
+            {"sync_value": [0x12, 0x34]},
+        ),
     ],
 )
 def test_radio_settings_checked(
@@ -154,7 +162,7 @@ def test_radio_settings_checked(
     fix: dict | None,
 ) -> None:
     """Packets vary in length; FSK or OOK on an SX127x needs packet mode, a sync word or preamble detection, and
-    holds at most 64 bytes.
+    holds at most 64 bytes; FSK on an SX126x needs a sync word.
     """
     config = {f"{domain}_id": "radio", CONF_MAX_PACKET_SIZE: 64, **link}
     token = fv.full_config.set(_FullConfig(domain, radio))
@@ -190,7 +198,7 @@ def test_radio_settings_checked(
 )
 def test_rx_start_needed_for_replies(setup_core, link: dict, match: str | None) -> None:
     """A radio that sleeps after sending suits only a link whose layers need no packets back."""
-    sleeping = {"payload_length": 0, "rx_start": False}
+    sleeping = _lora(payload_length=0, rx_start=False)
     config = sx126x_packet_interface.CONFIG_SCHEMA({"sx126x_id": "radio", **link})
     token = fv.full_config.set(_FullConfig("sx126x", sleeping))
     try: