diff --git a/esphome/components/packet_interface/layers/__init__.py b/esphome/components/packet_interface/layers/__init__.py
index 4f48f3c2b20..1daf62e9db5 100644
--- a/esphome/components/packet_interface/layers/__init__.py
+++ b/esphome/components/packet_interface/layers/__init__.py
@@ -51,6 +51,10 @@ class LayerKind:
         """Register a type with its schema."""
 
         def decorator(build: LayerBuilder) -> LayerBuilder:
+            if name in self.types:
+                raise ValueError(
+                    f"{self.key} layer type '{name}' is already registered"
+                )
             self.types[name] = LayerType(schema, build)
             return build
 
diff --git a/tests/unit_tests/test_packet_interface.py b/tests/unit_tests/test_packet_interface.py
index 4e184828424..de93673aadf 100644
--- a/tests/unit_tests/test_packet_interface.py
+++ b/tests/unit_tests/test_packet_interface.py
@@ -103,3 +103,17 @@ def test_registered_type_selectable(setup_core) -> None:
         assert RELIABILITY.get_type(config).build is build
     finally:
         del RELIABILITY.types["test"]
+
+
+def test_duplicate_layer_type_rejected(setup_core) -> None:
+    """Registering a type under a name already in use is an error, not a silent replacement."""
+
+    async def build(config: dict, lower: Any) -> Any:
+        return lower
+
+    RELIABILITY.register("test", schema=cv.Schema({}))(build)
+    try:
+        with pytest.raises(ValueError, match="already registered"):
+            RELIABILITY.register("test", schema=cv.Schema({}))(build)
+    finally:
+        del RELIABILITY.types["test"]