diff --git a/core/block.js b/core/block.js
index 0bace4292..a6986f7d5 100644
--- a/core/block.js
+++ b/core/block.js
@@ -127,6 +127,9 @@ Blockly.Block = function(workspace, prototypeName, opt_id) {
   this.workspace = workspace;
   /** @type {boolean} */
   this.isInFlyout = workspace.isFlyout;
+  /** @type {boolean} */
+  this.isInMutator = workspace.isMutator;
+
   /** @type {boolean} */
   this.RTL = workspace.RTL;
 
diff --git a/core/block_svg.js b/core/block_svg.js
index 719c967e5..656b61596 100644
--- a/core/block_svg.js
+++ b/core/block_svg.js
@@ -533,6 +533,12 @@ Blockly.BlockSvg.prototype.onMouseDown_ = function(e) {
   if (this.isInFlyout) {
     return;
   }
+  if (this.isInMutator) {
+    // Mutator's coordinate system could be out of date because the bubble was
+    // dragged, the block was moved, the parent workspace zoomed, etc.
+    this.workspace.resize();
+  }
+
   this.workspace.updateScreenCalculationsIfScrolled();
   this.workspace.markFocused();
   Blockly.terminateDrag_();
diff --git a/core/mutator.js b/core/mutator.js
index d5cca45e5..19a0fe86b 100644
--- a/core/mutator.js
+++ b/core/mutator.js
@@ -129,6 +129,7 @@ Blockly.Mutator.prototype.createEditor_ = function() {
     setMetrics: null
   };
   this.workspace_ = new Blockly.WorkspaceSvg(workspaceOptions);
+  this.workspace_.isMutator = true;
   this.svgDialog_.appendChild(
       this.workspace_.createDom('blocklyMutatorBackground'));
   return this.svgDialog_;
diff --git a/core/workspace_svg.js b/core/workspace_svg.js
index ff1476e78..9148c8338 100644
--- a/core/workspace_svg.js
+++ b/core/workspace_svg.js
@@ -82,6 +82,13 @@ Blockly.WorkspaceSvg.prototype.rendered = true;
  */
 Blockly.WorkspaceSvg.prototype.isFlyout = false;
 
+/**
+ * Is this workspace the surface for a mutator?
+ * @type {boolean}
+ * @package
+ */
+Blockly.WorkspaceSvg.prototype.isMutator = false;
+
 /**
  * Is this workspace currently being dragged around?
  * DRAG_NONE - No drag operation.