diff --git a/lib/schemaRegistry.js b/lib/schemaRegistry.js
index 6e3f0b0..77180f2 100644
--- a/lib/schemaRegistry.js
+++ b/lib/schemaRegistry.js
@@ -104,7 +104,10 @@ SchemaRegistry._gatherRefs = function(obj) {
   do {
 
     if (Object.prototype.hasOwnProperty.call(currentObj, '$ref')) {
-      result.push(currentObj.$ref);
+      var currentObjRef = currentObj.$ref;
+      if ( typeof currentObjRef === "string" ) {
+        result.push(currentObj.$ref);
+      }
     }
 
     var keys = Object.keys(currentObj);