diff --git a/js/intro/model/EFACIntroModel.js b/js/intro/model/EFACIntroModel.js
index 4f257588..09bd95f5 100644
--- a/js/intro/model/EFACIntroModel.js
+++ b/js/intro/model/EFACIntroModel.js
@@ -234,7 +234,7 @@ define( require => {
     );
 
     // @public - used to notify the view that a manual step was called
-    this.manualStepEmitter = new Emitter( { argumentTypes: [ { valueType: 'number' } ] } );
+    this.manualStepEmitter = new Emitter( { validators: [ { valueType: 'number' } ] } );
   }
 
   // helper function
diff --git a/js/systems/model/SystemsModel.js b/js/systems/model/SystemsModel.js
index fc49c584..f973bbce 100644
--- a/js/systems/model/SystemsModel.js
+++ b/js/systems/model/SystemsModel.js
@@ -97,7 +97,7 @@ define( require => {
       ];
 
       // @public - used to notify the view that a manual step was called
-      this.manualStepEmitter = new Emitter( { argumentTypes: [ { valueType: 'number' } ] } );
+      this.manualStepEmitter = new Emitter( { validators: [ { valueType: 'number' } ] } );
 
       // set isActive = true for the first element in each carousel
       this.carousels.forEach( carousel => {