diff --git a/pysnooper/tracer.py b/pysnooper/tracer.py
index 91927ef..95f9b74 100644
--- a/pysnooper/tracer.py
+++ b/pysnooper/tracer.py
@@ -225,7 +225,7 @@ class Tracer:
         self.target_frames.discard(calling_frame)
 
     def _is_internal_frame(self, frame):
-        return frame.f_code.co_filename == __file__
+        return frame.f_code.co_filename == Tracer.__enter__.__code__.co_filename
 
     def trace(self, frame, event, arg):