diff --git a/Lib/StringIO.py b/Lib/StringIO.py
index 5c463fb..1e5f254 100644
--- a/Lib/StringIO.py
+++ b/Lib/StringIO.py
@@ -72,8 +72,7 @@
         method is called repeatedly. This method returns the next input line,
         or raises StopIteration when EOF is hit.
         """
-        if self.closed:
-            raise StopIteration
+        _complain_ifclosed(self.closed)
         r = self.readline()
         if not r:
             raise StopIteration