diff --git a/src/wp-admin/includes/ms.php b/src/wp-admin/includes/ms.php
index 220d6323e3562..4c0668494ec66 100644
--- a/src/wp-admin/includes/ms.php
+++ b/src/wp-admin/includes/ms.php
@@ -98,7 +98,7 @@ function wpmu_delete_blog( $blog_id, $drop = false ) {
 	}
 
 	// Don't destroy the initial, main, or root blog.
-	if ( $drop && ( 1 == $blog_id || is_main_site( $blog_id ) || ( $blog->path == $current_network->path && $blog->domain == $current_network->domain ) ) ) {
+	if ( $drop && $blog && ( 1 == $blog_id || is_main_site( $blog_id ) || ( $blog->path == $current_network->path && $blog->domain == $current_network->domain ) ) ) {
 		$drop = false;
 	}
 
diff --git a/src/wp-includes/nav-menu.php b/src/wp-includes/nav-menu.php
index 6a290bdaa9e31..74214c6636440 100644
--- a/src/wp-includes/nav-menu.php
+++ b/src/wp-includes/nav-menu.php
@@ -1139,7 +1139,9 @@ 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;
 				}
 
@@ -1150,7 +1152,9 @@ 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 b0da967b8b9a3..d8fbd6b92fee9 100644
--- a/tests/phpunit/tests/menu/nav-menu.php
+++ b/tests/phpunit/tests/menu/nav-menu.php
@@ -200,4 +200,29 @@ function test_numerical_locations() {
 		);
 		$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 );
+	}
 }