diff --git a/js/gravity-force-lab-basics/view/ForceSoundGenerator.js b/js/gravity-force-lab-basics/view/ForceSoundGenerator.js
index e804232..577210a 100644
--- a/js/gravity-force-lab-basics/view/ForceSoundGenerator.js
+++ b/js/gravity-force-lab-basics/view/ForceSoundGenerator.js
@@ -9,8 +9,9 @@ define( require => {
   'use strict';
 
   // modules
-  const SoundClip = require( 'TAMBO/sound-generators/SoundClip' );
   const gravityForceLabBasics = require( 'GRAVITY_FORCE_LAB_BASICS/gravityForceLabBasics' );
+  const merge = require( 'PHET_CORE/merge' );
+  const SoundClip = require( 'TAMBO/sound-generators/SoundClip' );
 
   // constants
   const FADE_START_DELAY = 0.2; // in seconds, time to wait before starting fade
@@ -34,7 +35,7 @@ define( require => {
      */
     constructor( model, options ) {
 
-      options = _.extend( {
+      options = merge( {
         initialOutputLevel: 0.7,
         loop: true,
         trimSilence: false
diff --git a/js/gravity-force-lab-basics/view/GFLBMassControl.js b/js/gravity-force-lab-basics/view/GFLBMassControl.js
index ad63a91..572e749 100644
--- a/js/gravity-force-lab-basics/view/GFLBMassControl.js
+++ b/js/gravity-force-lab-basics/view/GFLBMassControl.js
@@ -13,6 +13,7 @@ define( require => {
   const GFLBConstants = require( 'GRAVITY_FORCE_LAB_BASICS/gravity-force-lab-basics/GFLBConstants' );
   const gravityForceLabBasics = require( 'GRAVITY_FORCE_LAB_BASICS/gravityForceLabBasics' );
   const HBox = require( 'SCENERY/nodes/HBox' );
+  const merge = require( 'PHET_CORE/merge' );
   const NumberPicker = require( 'SCENERY_PHET/NumberPicker' );
   const Panel = require( 'SUN/Panel' );
   const PhetFont = require( 'SCENERY_PHET/PhetFont' );
@@ -44,7 +45,7 @@ define( require => {
     constructor( titleString, valueProperty, massRange, labelContent, thisObjectEnum,
                  massDescriber, tandem, options ) {
 
-      options = _.extend( {
+      options = merge( {
         color: new Color( 0, 0, 255 )
       }, options );