diff --git a/Packages/viewerbase/client/components/viewer/viewportOverlay/viewportOverlay.js b/Packages/viewerbase/client/components/viewer/viewportOverlay/viewportOverlay.js
index 29cb8179e..82ce4d8a3 100644
--- a/Packages/viewerbase/client/components/viewer/viewportOverlay/viewportOverlay.js
+++ b/Packages/viewerbase/client/components/viewer/viewportOverlay/viewportOverlay.js
@@ -135,6 +135,10 @@ function getImage(viewportIndex) {
     return enabledElement.image;
 }
 
+function formatDateTime(date, time) {
+    return `${date} ${time}`;
+}
+
 Template.viewportOverlay.helpers({
     wwwc: function() {
         Session.get('CornerstoneImageRendered' + this.viewportIndex);
@@ -306,19 +310,18 @@ Template.viewportOverlay.helpers({
         }
 
         // Make sure there are more than two studies loaded in the viewer
-        //
+        var viewportStudies = ViewerStudies.find();
+        if (viewportStudies.count() < 2) {
+            return;
+        }
+
         // Here we sort the collection in ascending order by study date, so
         // that we can obtain the oldest study as the first element of the array
         //
         // TODO= Find out if we should encode studyDate as a Date in the ViewerStudies Collection
-        var viewportStudies = ViewerStudies.find({}, {
-            sort: {
-                studyDate: 1
-            }
+        var viewportStudiesArray = _.sortBy(viewportStudies.fetch(), function(study) {
+            return formatDateTime(study.studyDate, study.studyTime);
         });
-        if (viewportStudies.count() < 2) {
-            return;
-        }
 
         // Get study data
         var study = cornerstoneTools.metaData.get('study', this.imageId);
@@ -326,8 +329,8 @@ Template.viewportOverlay.helpers({
             return;
         }
 
-        var oldestStudy = viewportStudies.fetch()[0];
-        if ((study.studyDate + " " + study.studyTime) <= (oldestStudy.studyDate + " " + oldestStudy.studyTime)) {
+        var oldestStudy = viewportStudiesArray[0];
+        if (formatDateTime(study.studyDate, study.studyTime) <= formatDateTime(oldestStudy.studyDate, oldestStudy.studyTime)) {
             return 'Prior';
         }
     }