diff -r d3ddbad31b3e Lib/posixpath.py
--- a/Lib/posixpath.py	Wed May 09 14:59:24 2012 +0300
+++ b/Lib/posixpath.py	Wed May 09 19:46:49 2012 -0700
@@ -267,8 +267,8 @@
         except KeyError:
             return path
         userhome = pwent.pw_dir
-    userhome = userhome.rstrip('/') or userhome
-    return userhome + path[i:]
+    userhome = userhome.rstrip('/')
+    return userhome + path[i:] or '/'
 
 
 # Expand paths containing shell variable substitutions.
diff -r d3ddbad31b3e Lib/test/test_posixpath.py
--- a/Lib/test/test_posixpath.py	Wed May 09 14:59:24 2012 +0300
+++ b/Lib/test/test_posixpath.py	Wed May 09 19:46:49 2012 -0700
@@ -201,6 +201,7 @@
             with test_support.EnvironmentVarGuard() as env:
                 env['HOME'] = '/'
                 self.assertEqual(posixpath.expanduser("~"), "/")
+                self.assertEqual(posixpath.expanduser("~/foo"), "/foo")
 
     def test_normpath(self):
         self.assertEqual(posixpath.normpath(""), ".")