diff --git a/mozilla/xpcom/base/gqi.py b/mozilla/xpcom/base/gqi.py
index eb8a1a41e14..b2911d0123e 100644
--- a/mozilla/xpcom/base/gqi.py
+++ b/mozilla/xpcom/base/gqi.py
@@ -2,7 +2,7 @@
 
 """Implement QueryInterface using optimized generated code."""
 
-import os, errno, re, sys, sets
+import os, posixpath, errno, re, sys, sets
 
 # Global controlling debug output to sys.stderr
 debug = False
@@ -18,7 +18,7 @@ def findfile(f, curfile, includedirs):
     sdirs.extend(includedirs)
 
     for dir in sdirs:
-        t = os.path.join(dir, f)
+        t = posixpath.join(dir, f)
         if os.path.exists(t):
             return t