diff --git a/core/field.js b/core/field.js
index 279d19539..67a5c64ba 100644
--- a/core/field.js
+++ b/core/field.js
@@ -231,9 +231,9 @@ Blockly.Field.prototype.getSize = function() {
  */
 Blockly.Field.prototype.getScaledBBox_ = function() {
   var bBox = this.borderRect_.getBBox();
-  bBox.width *= this.sourceBlock_.workspace.scale;
-  bBox.height *= this.sourceBlock_.workspace.scale;
-  return bBox;
+  // Create new object, as getBBox can return an uneditable SVGRect.
+  return {width: bBox.width * this.sourceBlock_.workspace.scale,
+          height: bBox.height * this.sourceBlock_.workspace.scale};
 };
 
 /**
diff --git a/core/field_textinput.js b/core/field_textinput.js
index 3fdbacd0f..58db44915 100644
--- a/core/field_textinput.js
+++ b/core/field_textinput.js
@@ -228,10 +228,8 @@ Blockly.FieldTextInput.prototype.validate_ = function() {
 Blockly.FieldTextInput.prototype.resizeEditor_ = function() {
   var div = Blockly.WidgetDiv.DIV;
   var bBox = this.fieldGroup_.getBBox();
-  bBox.width *= this.sourceBlock_.workspace.scale;
-  bBox.height *= this.sourceBlock_.workspace.scale;
-  div.style.width = bBox.width + 'px';
-  div.style.height = bBox.height + 'px';
+  div.style.width = bBox.width * this.sourceBlock_.workspace.scale + 'px';
+  div.style.height = bBox.height * this.sourceBlock_.workspace.scale + 'px';
   var xy = this.getAbsoluteXY_();
   // In RTL mode block fields and LTR input fields the left edge moves,
   // whereas the right edge is fixed.  Reposition the editor.