diff -r 3b1dbe7a2aa0 Modules/zipimport.c
--- a/Modules/zipimport.c	Wed Apr 03 07:01:07 2013 -0400
+++ b/Modules/zipimport.c	Thu Apr 04 11:00:56 2013 +0100
@@ -349,7 +349,8 @@
     if (mi == MI_NOT_FOUND) {
         /* Not a module or regular package. See if this is a directory, and
            therefore possibly a portion of a namespace package. */
-        int is_dir = check_is_directory(self, self->prefix, fullname);
+        PyObject *subname = get_subname(fullname);
+        int is_dir = check_is_directory(self, self->prefix, subname);
         if (is_dir < 0)
             return -1;
         if (is_dir) {
@@ -358,7 +359,7 @@
                without a trailing separator. */
             *namespace_portion = PyUnicode_FromFormat("%U%c%U%U",
                                                       self->archive, SEP,
-                                                      self->prefix, fullname);
+                                                      self->prefix, subname);
             if (*namespace_portion == NULL)
                 return FL_ERROR;
             return FL_NS_FOUND;