diff --git a/mercurial/hgweb/wsgicgi.py b/mercurial/hgweb/wsgicgi.py
--- a/mercurial/hgweb/wsgicgi.py
+++ b/mercurial/hgweb/wsgicgi.py
@@ -77,7 +77,7 @@
                     # Re-raise original exception if headers sent
                     raise exc_info[0](exc_info[1], exc_info[2])
             finally:
-                exc_info = None  # avoid dangling circular ref
+                del exc_info  # avoid dangling circular ref
         elif headers_set:
             raise AssertionError(b"Headers already set!")