diff --git a/js/model/Charge.js b/js/model/Charge.js
index 02c78636..6e3c09aa 100644
--- a/js/model/Charge.js
+++ b/js/model/Charge.js
@@ -112,7 +112,7 @@ define( function( require ) {
      * @public
      */
     setLocation: function( circuitElement, distance ) {
-      assert && assert( !isFinite( distance ), 'Distance was not finite' ); // also guards against NaN
+      assert && assert( isFinite( distance ), 'Distance was not finite' ); // also guards against NaN
       assert && assert( circuitElement.containsScalarLocation( distance ), 'no location in branch' );
       this.circuitElement = circuitElement;
       this.distanceProperty.set( distance );