diff --git a/lib/OpenLayers/Format/WMTSCapabilities.js b/lib/OpenLayers/Format/WMTSCapabilities.js
index 157042cb55..aedd5e804d 100644
--- a/lib/OpenLayers/Format/WMTSCapabilities.js
+++ b/lib/OpenLayers/Format/WMTSCapabilities.js
@@ -159,7 +159,7 @@ OpenLayers.Format.WMTSCapabilities = OpenLayers.Class(OpenLayers.Format.XML.Vers
 
         var resolutions = [];
         if (config.isBaseLayer !== false) {
-            for (mid in matrixSet.matrixIds) {
+            for (var mid in matrixSet.matrixIds) {
                 if (matrixSet.matrixIds.hasOwnProperty(mid)) {
                     resolutions.push(
                         matrixSet.matrixIds[mid].scaleDenominator * 0.28E-3