diff --git src/wp-includes/js/customize-preview.js src/wp-includes/js/customize-preview.js
index a4cb196..42d0ba3 100644
--- src/wp-includes/js/customize-preview.js
+++ src/wp-includes/js/customize-preview.js
@@ -49,14 +49,14 @@
 		history.replaceState = ( function( nativeReplaceState ) {
 			return function historyReplaceState( data, title, url ) {
 				currentHistoryState = data;
-				return nativeReplaceState.call( history, data, title, injectUrlWithState( url ) );
+				return nativeReplaceState.call( history, data, title, ! _.isUndefined( url ) && null !== url ? injectUrlWithState( url ) : null );
 			};
 		} )( history.replaceState );
 
 		history.pushState = ( function( nativePushState ) {
 			return function historyPushState( data, title, url ) {
 				currentHistoryState = data;
-				return nativePushState.call( history, data, title, injectUrlWithState( url ) );
+				return nativePushState.call( history, data, title, ! _.isUndefined( url ) && null !== url ? injectUrlWithState( url ) : null );
 			};
 		} )( history.pushState );