diff --git a/js/accessibility/Accessibility.js b/js/accessibility/Accessibility.js
index 18e647387..de529c514 100644
--- a/js/accessibility/Accessibility.js
+++ b/js/accessibility/Accessibility.js
@@ -561,7 +561,9 @@ define( function( require ) {
             assert && assert( this._accessibleVisible, 'trying to set focus on a node with invisible accessible content' );
             assert && assert( this._accessibleInstances.length === 1, 'focus() unsupported for Nodes using DAG, accessible content is not unique' );
 
-            this._accessibleInstances[ 0 ].peer.primarySibling.focus();
+            var peer = this._accessibleInstances[ 0 ].peer;
+            assert && assert( peer, 'must have a peer to focus' );
+            peer.focus();
           }
         },
 
diff --git a/js/accessibility/AccessiblePeer.js b/js/accessibility/AccessiblePeer.js
index 134936972..05fe9e196 100644
--- a/js/accessibility/AccessiblePeer.js
+++ b/js/accessibility/AccessiblePeer.js
@@ -291,6 +291,14 @@ define( function( require ) {
       return document.activeElement === this.primarySibling;
     },
 
+    /**
+     * Focus the primary sibling of the peer.
+     */
+    focus: function() {
+      assert && assert( this.primarySibling, 'must have a primary sibling to focus' );
+      this.primarySibling.focus();
+    },
+
 
     /**
      * Removes external references from this peer, and places it in the pool.