diff --git a/src/_pytest/recwarn.py b/src/_pytest/recwarn.py
index e89fecd12..ec91bc484 100644
--- a/src/_pytest/recwarn.py
+++ b/src/_pytest/recwarn.py
@@ -42,13 +42,11 @@ def recwarn() -> Generator["WarningsRecorder", None, None]:
 @overload
 def deprecated_call(
     *, match: Optional[Union[str, Pattern[str]]] = ...
-) -> "WarningsRecorder":
-    ...
+) -> "WarningsRecorder": ...
 
 
 @overload
-def deprecated_call(func: Callable[..., T], *args: Any, **kwargs: Any) -> T:
-    ...
+def deprecated_call(func: Callable[..., T], *args: Any, **kwargs: Any) -> T: ...
 
 
 def deprecated_call(
@@ -90,8 +88,7 @@ def warns(
     expected_warning: Union[Type[Warning], Tuple[Type[Warning], ...]] = ...,
     *,
     match: Optional[Union[str, Pattern[str]]] = ...,
-) -> "WarningsChecker":
-    ...
+) -> "WarningsChecker": ...
 
 
 @overload
@@ -100,8 +97,7 @@ def warns(
     func: Callable[..., T],
     *args: Any,
     **kwargs: Any,
-) -> T:
-    ...
+) -> T: ...
 
 
 def warns(
@@ -336,7 +332,9 @@ class WarningsChecker(WarningsRecorder):
 
     @staticmethod
     def _validate_message(wrn: Any) -> None:
-        if not isinstance(msg := wrn.message.args[0], str):
+        if type(wrn.message) is UserWarning and not isinstance(
+            msg := wrn.message.args[0], str
+        ):
             raise TypeError(
                 f"Warning message must be str, got {msg!r} (type {type(msg).__name__})"
             )