diff --git a/image/test/unit/test_imgtools.js b/image/test/unit/test_imgtools.js
index f7bd7c1c5074..25e72fa0a789 100644
--- a/image/test/unit/test_imgtools.js
+++ b/image/test/unit/test_imgtools.js
@@ -130,7 +130,7 @@ if (!imgTools)
 // different set of reference images. nsIXULRuntime.OS doesn't seem to be
 // available in xpcshell, so we'll use this as a kludgy way to figure out if
 // we're running on Windows.
-var isWindows = ("@mozilla.org/windows-registry-key;1" in Cc);
+var isWindows = mozinfo.os == "win";
 
 
 /* ========== 1 ========== */