diff --git a/node_modules/c9/urls.js b/node_modules/c9/urls.js
index 7484194b..0be2eb00 100644
--- a/node_modules/c9/urls.js
+++ b/node_modules/c9/urls.js
@@ -36,6 +36,8 @@ plugin.getBaseUrl = function(req, sourceBaseUrlPattern, targetBaseUrlPattern) {
         || req;
     if (typeof sourceHost !== "string")
         throw new Error("Not a valid request object: " + req);
+    if (!sourceBaseUrlPattern)
+        throw new Error("getBaseUrls() requires at least two arguments");
 
     var sourceHostMatcher = sourceBaseUrlPattern
         .replace(/^https?:\/\//, "")