diff --git a/src/wp-includes/class-wp-customize-nav-menus.php b/src/wp-includes/class-wp-customize-nav-menus.php
index fdf45e52297f3..9b24fa0b67b2f 100644
--- a/src/wp-includes/class-wp-customize-nav-menus.php
+++ b/src/wp-includes/class-wp-customize-nav-menus.php
@@ -1265,14 +1265,14 @@ public function filter_wp_nav_menu_args( $args ) {
 	 *
 	 * @param string $nav_menu_content The HTML content for the navigation menu.
 	 * @param object $args             An object containing wp_nav_menu() arguments.
-	 * @return null
+	 * @return string Nav menu HTML with selective refresh attributes added if partial can be refreshed.
 	 */
 	public function filter_wp_nav_menu( $nav_menu_content, $args ) {
 		if ( isset( $args->customize_preview_nav_menus_args['can_partial_refresh'] ) && $args->customize_preview_nav_menus_args['can_partial_refresh'] ) {
 			$attributes = sprintf( ' data-customize-partial-id="%s"', esc_attr( 'nav_menu_instance[' . $args->customize_preview_nav_menus_args['args_hmac'] . ']' ) );
 			$attributes .= ' data-customize-partial-type="nav_menu_instance"';
 			$attributes .= sprintf( ' data-customize-partial-placement-context="%s"', esc_attr( wp_json_encode( $args->customize_preview_nav_menus_args ) ) );
-			$nav_menu_content = preg_replace( '#^(<\w+)#', '$1 ' . $attributes, $nav_menu_content, 1 );
+			$nav_menu_content = preg_replace( '#^(<\w+)#', '$1 ' . str_replace( '\\', '\\\\', $attributes ), $nav_menu_content, 1 );
 		}
 		return $nav_menu_content;
 	}
diff --git a/tests/phpunit/tests/customize/nav-menus.php b/tests/phpunit/tests/customize/nav-menus.php
index 77116305e2b77..393790af43ef9 100644
--- a/tests/phpunit/tests/customize/nav-menus.php
+++ b/tests/phpunit/tests/customize/nav-menus.php
@@ -861,19 +861,27 @@ function test_filter_wp_nav_menu_args() {
 	/**
 	 * Test the filter_wp_nav_menu method.
 	 *
-	 * @see WP_Customize_Nav_Menus::filter_wp_nav_menu()
+	 * @covers WP_Customize_Nav_Menus::filter_wp_nav_menu()
+	 * @covers WP_Customize_Nav_Menus::filter_wp_nav_menu_args()
 	 */
 	function test_filter_wp_nav_menu() {
 		do_action( 'customize_register', $this->wp_customize );
 		$menus = new WP_Customize_Nav_Menus( $this->wp_customize );
 
-		$args = $menus->filter_wp_nav_menu_args( array(
+		$original_args = array(
 			'echo'        => true,
 			'menu'        => wp_create_nav_menu( 'Foo' ),
 			'fallback_cb' => 'wp_page_menu',
 			'walker'      => '',
 			'items_wrap'  => '<ul id="%1$s" class="%2$s">%3$s</ul>',
-		) );
+		);
+
+		// Add global namespace prefix to check #41488.
+		if ( version_compare( PHP_VERSION, '5.3', '>=' ) ) {
+			$original_args['fallback_cb'] = '\\' . $original_args['fallback_cb'];
+		}
+
+		$args = $menus->filter_wp_nav_menu_args( $original_args );
 
 		ob_start();
 		wp_nav_menu( $args );
@@ -883,7 +891,10 @@ function test_filter_wp_nav_menu() {
 
 		$this->assertContains( sprintf( ' data-customize-partial-id="nav_menu_instance[%s]"', $args['customize_preview_nav_menus_args']['args_hmac'] ), $result );
 		$this->assertContains( ' data-customize-partial-type="nav_menu_instance"', $result );
-		$this->assertContains( ' data-customize-partial-placement-context="', $result );
+		$this->assertTrue( (bool) preg_match( '/data-customize-partial-placement-context="(.+?)"/', $result, $matches ) );
+		$context = json_decode( html_entity_decode( $matches[1] ), true );
+		$this->assertEquals( $original_args, wp_array_slice_assoc( $context, array_keys( $original_args ) ) ); // Because assertArraySubset is not available in PHP 5.2.
+		$this->assertTrue( $context['can_partial_refresh'] );
 	}
 
 	/**