diff --git a/fastapi/sse.py b/fastapi/sse.py
index 55d668b4bd..fc0c31f140 100644
--- a/fastapi/sse.py
+++ b/fastapi/sse.py
@@ -264,9 +264,7 @@ def get_sse_data_type(annotation: Any) -> Any | None:
     if annotation is ServerSentEvent:
         return None
     meta = getattr(annotation, "__pydantic_generic_metadata__", None)
-    if not meta:
-        return None
-    args = meta.get("args", ())
+    args = meta.get("args", ()) if meta else ()
     if not args or isinstance(args[0], TypeVar):
         return None
     return args[0]
diff --git a/tests/test_sse.py b/tests/test_sse.py
index bc464c464e..8866a669e1 100644
--- a/tests/test_sse.py
+++ b/tests/test_sse.py
@@ -340,6 +340,15 @@ def test_get_sse_data_type_non_sse():
     assert get_sse_data_type(None) is None
 
 
+def test_get_sse_data_type_subclass_no_type_param():
+    """get_sse_data_type returns None for a plain ServerSentEvent subclass."""
+
+    class MyEvent(ServerSentEvent):
+        pass
+
+    assert get_sse_data_type(MyEvent) is None
+
+
 def test_generic_sse_construction_validates_data():
     """ServerSentEvent[Item] requires data to be an Item."""
     item = Item(name="Foo", description=None)