diff --git a/importlib_resources/_common.py b/importlib_resources/_common.py
index 364e4c0..0566035 100644
--- a/importlib_resources/_common.py
+++ b/importlib_resources/_common.py
@@ -87,19 +87,13 @@ def _(cand: None) -> types.ModuleType:
     return resolve(_infer_caller().f_globals['__name__'])
 
 
-@functools.lru_cache
-def _this_filename():
-    frame = inspect.currentframe()
-    return __file__ if frame is None else inspect.getframeinfo(frame).filename
-
-
 def _infer_caller():
     """
     Walk the stack and find the frame of the first caller not in this module.
     """
 
     def is_this_file(frame_info):
-        return frame_info.filename == _this_filename()
+        return frame_info.filename == __file__.replace('.pyc', '.py')
 
     def is_wrapper(frame_info):
         return frame_info.function == 'wrapper'