diff --git a/layout/tools/reftest/reftest.jsm b/layout/tools/reftest/reftest.jsm
index a15dac93fc04..ad78873d7360 100644
--- a/layout/tools/reftest/reftest.jsm
+++ b/layout/tools/reftest/reftest.jsm
@@ -714,6 +714,12 @@ function BuildConditionSandbox(aURL) {
     sandbox.webrtc = false;
 #endif
 
+#ifdef MOZ_STYLO
+    sandbox.stylo = true;
+#else
+    sandbox.stylo = false;
+#endif
+
     var hh = CC[NS_NETWORK_PROTOCOL_CONTRACTID_PREFIX + "http"].
                  getService(CI.nsIHttpProtocolHandler);
     var httpProps = ["userAgent", "appName", "appVersion", "vendor",