diff --git a/Lib/warnings.py b/Lib/warnings.py
index 5eac60f7c5b..8baac479cd2 100644
--- a/Lib/warnings.py
+++ b/Lib/warnings.py
@@ -63,7 +63,7 @@ def warn(message, category=None, stacklevel=1):
 def warn_explicit(message, category, filename, lineno,
                   module=None, registry=None):
     if module is None:
-        module = filename
+        module = filename or "<unknown>"
         if module[-3:].lower() == ".py":
             module = module[:-3] # XXX What about leading pathname?
     if registry is None:
diff --git a/Misc/NEWS b/Misc/NEWS
index 6729ea8a794..a95774fcec9 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -335,6 +335,9 @@ Extension Modules
 Library
 -------
 
+- Bug #1403410: The warnings module now doesn't get confused
+  when it can't find out the module name it generates a warning for.
+  
 - Patch #1177307: Added a new codec utf_8_sig for UTF-8 with a BOM signature.
 
 - Patch #1157027: cookielib mishandles RFC 2109 cookies in Netscape mode