diff --git a/core/mutator.js b/core/mutator.js
index 0f35789f3..b459cab58 100644
--- a/core/mutator.js
+++ b/core/mutator.js
@@ -202,8 +202,7 @@ Blockly.Mutator.prototype.updateEditable = function() {
 };
 
 /**
- * Callback function triggered when the bubble has resized.
- * Resize the workspace accordingly.
+ * Resize the bubble to match the size of the workspace.
  * @private
  */
 Blockly.Mutator.prototype.resizeBubble_ = function() {
@@ -294,6 +293,7 @@ Blockly.Mutator.prototype.setVisible = function(visible) {
       };
       this.block_.workspace.addChangeListener(this.sourceListener_);
     }
+    this.resizeBubble_();
     // When the mutator's workspace changes, update the source block.
     this.workspace_.addChangeListener(this.workspaceChanged_.bind(this));
     this.updateColour();