diff --git a/core/workspace_svg.js b/core/workspace_svg.js
index 3614e65ed..0194925c9 100644
--- a/core/workspace_svg.js
+++ b/core/workspace_svg.js
@@ -1105,6 +1105,9 @@ Blockly.WorkspaceSvg.prototype.setScale = function(newScale) {
     // No toolbox, resize flyout.
     this.flyout_.reflow();
   }
+  // This event has been handled.  Don't start a workspace drag.
+  e.stopPropagation();
+  e.preventDefault();
 };
 
 /**
diff --git a/core/zoom_controls.js b/core/zoom_controls.js
index 31a0b2126..f745c9c21 100644
--- a/core/zoom_controls.js
+++ b/core/zoom_controls.js
@@ -166,10 +166,12 @@ Blockly.ZoomControls.prototype.createDom = function() {
   Blockly.bindEvent_(zoominSvg, 'mousedown', null, function(e) {
     workspace.zoomCenter(1);
     e.stopPropagation();  // Don't start a workspace scroll.
+    e.preventDefault();
   });
   Blockly.bindEvent_(zoomoutSvg, 'mousedown', null, function(e) {
     workspace.zoomCenter(-1);
     e.stopPropagation();  // Don't start a workspace scroll.
+    e.preventDefault();
   });
 
   return this.svgGroup_;