diff --git a/index.js b/index.js
index <HASH>..<HASH> 100644
--- a/index.js
+++ b/index.js
@@ -28,7 +28,7 @@ function _getManifestData(file, opts) {
         if (_.isObject(json)) {
             var isRev = 1;
             Object.keys(json).forEach(function (key) {
-                if ( path.basename(json[key]).replace(new RegExp( opts.revSuffix ), '' ) !==  path.basename(key) ) {
+                if ( !_.isString(json[key]) || path.basename(json[key]).replace(new RegExp( opts.revSuffix ), '' ) !==  path.basename(key) ) {
                     isRev = 0;
                 }
             });
Fix issue where rev detection fails with additional JSON files