diff --git a/wp-includes/nav-menu.php b/wp-includes/nav-menu.php
index 79f89d62d1..9b6eeba9b3 100644
--- a/wp-includes/nav-menu.php
+++ b/wp-includes/nav-menu.php
@@ -1186,7 +1186,9 @@ function wp_map_nav_menu_locations( $new_nav_menu_locations, $old_nav_menu_locat
 			foreach ( $registered_nav_menus as $new_location => $name ) {
 
 				// ...actually match!
-				if ( false === stripos( $new_location, $slug ) && false === stripos( $slug, $new_location ) ) {
+				if ( is_string( $new_location ) && false === stripos( $new_location, $slug ) && false === stripos( $slug, $new_location ) ) {
+					continue;
+				} elseif ( is_numeric( $new_location ) && $new_location !== $slug ) {
 					continue;
 				}
 
@@ -1197,7 +1199,9 @@ function wp_map_nav_menu_locations( $new_nav_menu_locations, $old_nav_menu_locat
 					foreach ( $slug_group as $slug ) {
 
 						// ... have a match as well.
-						if ( false === stripos( $location, $slug ) && false === stripos( $slug, $location ) ) {
+						if ( is_string( $location ) && false === stripos( $location, $slug ) && false === stripos( $slug, $location ) ) {
+							continue;
+						} elseif ( is_numeric( $location ) && $location !== $slug ) {
 							continue;
 						}
 
diff --git a/wp-includes/version.php b/wp-includes/version.php
index c9eb662959..b83fccd353 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.1-alpha-44166';
+$wp_version = '5.1-alpha-44167';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.