diff --git a/stdlib/3/_importlib_modulespec.pyi b/stdlib/3/_importlib_modulespec.pyi
index 6ce54917024f..eca7a3252ca2 100644
--- a/stdlib/3/_importlib_modulespec.pyi
+++ b/stdlib/3/_importlib_modulespec.pyi
@@ -4,17 +4,22 @@
 # - ModuleType in types
 # - Loader in importlib.abc
 # - ModuleSpec in importlib.machinery (3.4 and later only)
+#
+# _Loader is the PEP-451-defined interface for a loader type/object.
 
 from abc import ABCMeta
 import sys
-from typing import Any, Dict, List, Optional
+from typing import Any, Dict, List, Optional, Protocol
+
+class _Loader(Protocol):
+    def load_module(self, fullname: str) -> ModuleType: ...
 
 class ModuleSpec:
     def __init__(self, name: str, loader: Optional[Loader], *,
                  origin: Optional[str] = ..., loader_state: Any = ...,
                  is_package: Optional[bool] = ...) -> None: ...
     name = ...  # type: str
-    loader = ...  # type: Optional[Loader]
+    loader = ...  # type: Optional[_Loader]
     origin = ...  # type: Optional[str]
     submodule_search_locations = ...  # type: Optional[List[str]]
     loader_state = ...  # type: Any
@@ -26,7 +31,7 @@ class ModuleType:
     __name__ = ...  # type: str
     __file__ = ...  # type: str
     __dict__ = ...  # type: Dict[str, Any]
-    __loader__ = ...  # type: Optional[Loader]
+    __loader__ = ...  # type: Optional[_Loader]
     __package__ = ...  # type: Optional[str]
     __spec__ = ...  # type: Optional[ModuleSpec]
     def __init__(self, name: str, doc: Optional[str] = ...) -> None: ...