diff --git a/Lib/test/regrtest.py b/Lib/test/regrtest.py
index ec39936..cd2442d 100755
--- a/Lib/test/regrtest.py
+++ b/Lib/test/regrtest.py
@@ -133,7 +133,7 @@
                 if r not in RESOURCE_NAMES:
                     usage(1, 'Invalid -u/--use option: ' + a)
                 if r not in use_resources:
-                    use_resources.extend(r)
+                    use_resources.append(r)
     if generate and verbose:
         usage(2, "-g and -v don't go together!")