diff --git a/dicomViewer.js b/dicomViewer.js
index 71187a6..13bfbf1 100644
--- a/dicomViewer.js
+++ b/dicomViewer.js
@@ -793,9 +793,11 @@ function keyDownHandler(e, element) {
             break;
         case 38: // Up
             manualScrollDicom(1, element);
+            e.preventDefault();
             break;
         case 40: // down
             manualScrollDicom(-1, element);
+            e.preventDefault();
             break;
         case 46: // .
             //toggleFlagged();