diff --git a/.travis.yml b/.travis.yml
index e8a677d3af..39d61d6416 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -12,11 +12,11 @@ env:
     - WP_TRAVISCI=travis:phpunit
 matrix:
   include:
-  - php: 7.3
   - php: 7.2
     env: WP_TRAVISCI=travis:format
   - php: 7.1
     env: WP_TRAVISCI=travis:js
+  - php: 7.3
   - php: 7.2
   - php: 7.1
   - php: 7.0
@@ -34,7 +34,6 @@ matrix:
   - php: nightly
   allow_failures:
   - php: nightly
-  - php: 7.3
 before_install:
 - |
   if [[ "$WP_TRAVISCI" == "travis:phpunit" ]]; then
diff --git a/src/wp-includes/nav-menu.php b/src/wp-includes/nav-menu.php
index 79f89d62d1..9b6eeba9b3 100644
--- a/src/wp-includes/nav-menu.php
+++ b/src/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/tests/phpunit/tests/menu/nav-menu.php b/tests/phpunit/tests/menu/nav-menu.php
index 57086afc28..b0b5c446fb 100644
--- a/tests/phpunit/tests/menu/nav-menu.php
+++ b/tests/phpunit/tests/menu/nav-menu.php
@@ -200,4 +200,29 @@ class Tests_Nav_Menu_Theme_Change extends WP_UnitTestCase {
 		);
 		$this->assertEqualSets( $expected_nav_menu_locations, $new_next_theme_nav_menu_locations );
 	}
+
+	/**
+	 * Technically possible old nav menu locations were registered numerically.
+	 *
+	 * @covers wp_map_nav_menu_locations()
+	 */
+	public function test_numerical_old_locations() {
+		$this->register_nav_menu_locations( array( 'primary', 1 ) );
+
+		$old_nav_menu_locations = array(
+			'primary'  => 1,
+			'tertiary' => 2,
+			0          => 3,
+		);
+
+		$next_theme_nav_menu_locations     = array();
+		$new_next_theme_nav_menu_locations = wp_map_nav_menu_locations( $next_theme_nav_menu_locations, $old_nav_menu_locations );
+
+		$expected_nav_menu_locations = array(
+			'primary' => 1,
+			0         => 3,
+		);
+
+		$this->assertEqualSets( $expected_nav_menu_locations, $new_next_theme_nav_menu_locations );
+	}
 }