diff --git a/Lib/test/test_ntpath.py b/Lib/test/test_ntpath.py
index ae9054b..11f2f44 100644
--- a/Lib/test/test_ntpath.py
+++ b/Lib/test/test_ntpath.py
@@ -37,6 +37,12 @@
 
 tester('ntpath.abspath("C:\\")', "C:\\")
 
+tester('ntpath.commonprefix(["/home/swenson/spam", "/home/swen/spam"])',
+       "/home/swen")
+tester('ntpath.commonprefix(["\\home\\swen\\spam", "\\home\\swen\\eggs"])',
+       "\\home\\swen\\")
+tester('ntpath.commonprefix(["/home/swen/spam", "/home/swen/spam"])',
+       "/home/swen/spam")
 
 if errors:
 	print str(errors) + " errors."