diff --git a/js/model/Atom2.js b/js/model/Atom2.js
index fdb803f9..d9eebaef 100644
--- a/js/model/Atom2.js
+++ b/js/model/Atom2.js
@@ -37,8 +37,8 @@ define( function( require ) {
     this.addedToModelProperty = new BooleanProperty( true );
 
     // @public {Emitter} - Called with one parameter: particle
-    this.grabbedByUserEmitter = new Emitter( { argumentTypes: [ { valueType: Atom2 } ] } );
-    this.droppedByUserEmitter = new Emitter( { argumentTypes: [ { valueType: Atom2 } ] } );
+    this.grabbedByUserEmitter = new Emitter( { validators: [ { valueType: Atom2 } ] } );
+    this.droppedByUserEmitter = new Emitter( { validators: [ { valueType: Atom2 } ] } );
     this.removedFromModelEmitter = new Emitter(); //REVIEW: Umm, not triggered?
 
     this.tickEmitter = tickEmitter;