diff --git a/blockly_compressed.js b/blockly_compressed.js
index 87f876ef4..70620a5a5 100644
--- a/blockly_compressed.js
+++ b/blockly_compressed.js
@@ -863,7 +863,8 @@ Blockly.Connection.prototype.highlight=function(){var a;this.type==Blockly.INPUT
 {"class":"blocklyHighlightedConnectionPath",d:a,transform:"translate("+(this.x_-b.x)+", "+(this.y_-b.y)+")"},this.sourceBlock_.getSvgRoot())};Blockly.Connection.prototype.unhighlight=function(){goog.dom.removeNode(Blockly.Connection.highlightedPath_);delete Blockly.Connection.highlightedPath_};
 Blockly.Connection.prototype.tighten_=function(){var a=Math.round(this.targetConnection.x_-this.x_),b=Math.round(this.targetConnection.y_-this.y_);if(0!=a||0!=b){var c=this.targetBlock(),d=c.getSvgRoot();if(!d)throw"block is not rendered.";d=Blockly.getRelativeXY_(d);c.getSvgRoot().setAttribute("transform","translate("+(d.x-a)+", "+(d.y-b)+")");c.moveConnections_(-a,-b)}};
 Blockly.Connection.prototype.closest=function(a,b,c){function d(b){var c=e[b];if((c.type==Blockly.OUTPUT_VALUE||c.type==Blockly.PREVIOUS_STATEMENT)&&c.targetConnection||c.type==Blockly.INPUT_VALUE&&c.targetConnection&&!c.targetBlock().isMovable()||!p.checkType_(c))return!0;c=c.sourceBlock_;do{if(l==c)return!0;c=c.getParent()}while(c);var d=f-e[b].x_,c=g-e[b].y_,d=Math.sqrt(d*d+c*c);d<=a&&(k=e[b],a=d);return c<a}if(this.targetConnection)return{connection:null,radius:a};var e=this.dbList_[Blockly.OPPOSITE_TYPE[this.type]],
-f=this.x_+b,g=this.y_+c;b=0;for(var h=c=e.length-2;b<h;)e[h].y_<g?b=h:c=h,h=Math.floor((b+c)/2);c=b=h;var k=null,l=this.sourceBlock_,p=this;if(e.length){for(;0<=b&&d(b);)b--;do c++;while(c<e.length&&d(c))}return{connection:k,radius:a}};Blockly.Connection.prototype.checkType_=function(a){if(!this.check_||!a.check_)return!0;for(var b=0;b<this.check_.length;b++)if(-1!=a.check_.indexOf(this.check_[b]))return!0;return!1};
+f=this.x_+b,g=this.y_+c;b=0;for(var h=c=e.length-2;b<h;)e[h].y_<g?b=h:c=h,h=Math.floor((b+c)/2);c=b=h;var k=null,l=this.sourceBlock_,p=this;if(e.length){for(;0<=b&&d(b);)b--;do c++;while(c<e.length&&d(c))}return{connection:k,radius:a}};
+Blockly.Connection.prototype.checkType_=function(a){var b=this.targetBlock();if(b&&!b.isMovable()&&!this.sourceBlock_.isMovable()||(b=a.targetBlock())&&!b.isMovable()&&!a.sourceBlock_.isMovable())return!1;if(!this.check_||!a.check_)return!0;for(b=0;b<this.check_.length;b++)if(-1!=a.check_.indexOf(this.check_[b]))return!0;return!1};
 Blockly.Connection.prototype.setCheck=function(a){a?(goog.isArray(a)||(a=[a]),this.check_=a,this.targetConnection&&!this.checkType_(this.targetConnection)&&(this.isSuperior()?this.targetBlock().setParent(null):this.sourceBlock_.setParent(null),this.sourceBlock_.bumpNeighbours_())):this.check_=null;return this};
 Blockly.Connection.prototype.neighbours_=function(a){function b(b){var f=d-c[b].x_,g=e-c[b].y_;Math.sqrt(f*f+g*g)<=a&&k.push(c[b]);return g<a}for(var c=this.dbList_[Blockly.OPPOSITE_TYPE[this.type]],d=this.x_,e=this.y_,f=0,g=c.length-2,h=g;f<h;)c[h].y_<e?f=h:g=h,h=Math.floor((f+g)/2);var g=f=h,k=[];if(c.length){for(;0<=f&&b(f);)f--;do g++;while(g<c.length&&b(g))}return k};
 Blockly.Connection.prototype.hideAll=function(){this.inDB_&&this.dbList_[this.type].removeConnection_(this);if(this.targetConnection)for(var a=this.targetBlock().getDescendants(),b=0;b<a.length;b++){for(var c=a[b],d=c.getConnections_(!0),e=0;e<d.length;e++){var f=d[e];f.inDB_&&this.dbList_[f.type].removeConnection_(f)}c=c.getIcons();for(d=0;d<c.length;d++)c[d].setVisible(!1)}};
@@ -875,7 +876,7 @@ Blockly.ConnectionDB.init=function(a){var b=[];b[Blockly.INPUT_VALUE]=new Blockl
 Blockly.Field=function(a){this.size_=new goog.math.Size(0,25);this.setText(a)};Blockly.Field.prototype.sourceBlock_=null;Blockly.Field.prototype.visible_=!0;Blockly.Field.prototype.clone=function(){goog.asserts.fail("There should never be an instance of Field, only its derived classes.")};Blockly.Field.NBSP="\u00a0";Blockly.Field.prototype.EDITABLE=!0;
 Blockly.Field.prototype.init=function(a){this.sourceBlock_||(this.sourceBlock_=a,this.fieldGroup_=Blockly.createSvgElement("g",{},null),this.visible_||(this.fieldGroup_.style.display="none"),this.borderRect_=Blockly.createSvgElement("rect",{rx:4,ry:4,x:-Blockly.BlockSvg.SEP_SPACE_X/2,y:-12,height:16},this.fieldGroup_),this.textElement_=Blockly.createSvgElement("text",{"class":"blocklyText"},this.fieldGroup_),this.updateEditable(),a.getSvgRoot().appendChild(this.fieldGroup_),this.mouseUpWrapper_=Blockly.bindEvent_(this.fieldGroup_,
 "mouseup",this,this.onMouseUp_),this.updateTextNode_())};Blockly.Field.prototype.dispose=function(){this.mouseUpWrapper_&&(Blockly.unbindEvent_(this.mouseUpWrapper_),this.mouseUpWrapper_=null);this.sourceBlock_=null;goog.dom.removeNode(this.fieldGroup_);this.borderRect_=this.textElement_=this.fieldGroup_=null};
-Blockly.Field.prototype.updateEditable=function(){this.EDITABLE&&(this.sourceBlock_.isEditable()?(Blockly.addClass_(this.fieldGroup_,"blocklyEditableText"),Blockly.removeClass_(this.fieldGroup_,"blocklyNoNEditableText"),this.fieldGroup_.style.cursor=this.CURSOR):(Blockly.addClass_(this.fieldGroup_,"blocklyNonEditableText"),Blockly.removeClass_(this.fieldGroup_,"blocklyEditableText"),this.fieldGroup_.style.cursor=""))};Blockly.Field.prototype.isVisible=function(){return this.visible_};
+Blockly.Field.prototype.updateEditable=function(){this.EDITABLE&&this.sourceBlock_&&(this.sourceBlock_.isEditable()?(Blockly.addClass_(this.fieldGroup_,"blocklyEditableText"),Blockly.removeClass_(this.fieldGroup_,"blocklyNoNEditableText"),this.fieldGroup_.style.cursor=this.CURSOR):(Blockly.addClass_(this.fieldGroup_,"blocklyNonEditableText"),Blockly.removeClass_(this.fieldGroup_,"blocklyEditableText"),this.fieldGroup_.style.cursor=""))};Blockly.Field.prototype.isVisible=function(){return this.visible_};
 Blockly.Field.prototype.setVisible=function(a){if(this.visible_!=a){this.visible_=a;var b=this.getSvgRoot();b&&(b.style.display=a?"block":"none",this.render_())}};Blockly.Field.prototype.getSvgRoot=function(){return this.fieldGroup_};
 Blockly.Field.prototype.render_=function(){if(this.visible_&&this.textElement_){try{var a=this.textElement_.getComputedTextLength()}catch(b){a=8*this.textElement_.textContent.length}this.borderRect_&&this.borderRect_.setAttribute("width",a+Blockly.BlockSvg.SEP_SPACE_X)}else a=0;this.size_.width=a};Blockly.Field.prototype.getSize=function(){this.size_.width||this.render_();return this.size_};Blockly.Field.prototype.getText=function(){return this.text_};
 Blockly.Field.prototype.setText=function(a){null!==a&&a!==this.text_&&(this.text_=a,this.updateTextNode_(),this.sourceBlock_&&this.sourceBlock_.rendered&&(this.sourceBlock_.render(),this.sourceBlock_.bumpNeighbours_(),this.sourceBlock_.workspace.fireChangeEvent()))};
diff --git a/core/connection.js b/core/connection.js
index bef05407b..215ddc833 100644
--- a/core/connection.js
+++ b/core/connection.js
@@ -525,6 +525,17 @@ Blockly.Connection.prototype.closest = function(maxLimit, dx, dy) {
  * @private
  */
 Blockly.Connection.prototype.checkType_ = function(otherConnection) {
+  // Don't split a connection where both sides are immovable.
+  var thisTargetBlock = this.targetBlock();
+  if (thisTargetBlock && !thisTargetBlock.isMovable() &&
+      !this.sourceBlock_.isMovable()) {
+    return false;
+  }
+  var otherTargetBlock = otherConnection.targetBlock();
+  if (otherTargetBlock && !otherTargetBlock.isMovable() &&
+      !otherConnection.sourceBlock_.isMovable()) {
+    return false;
+  }
   if (!this.check_ || !otherConnection.check_) {
     // One or both sides are promiscuous enough that anything will fit.
     return true;
diff --git a/core/field.js b/core/field.js
index e8046630b..39ae22157 100644
--- a/core/field.js
+++ b/core/field.js
@@ -128,7 +128,7 @@ Blockly.Field.prototype.dispose = function() {
  * Add or remove the UI indicating if this field is editable or not.
  */
 Blockly.Field.prototype.updateEditable = function() {
-  if (!this.EDITABLE) {
+  if (!this.EDITABLE || !this.sourceBlock_) {
     return;
   }
   if (this.sourceBlock_.isEditable()) {