diff --git a/src/wp-includes/rewrite.php b/src/wp-includes/rewrite.php
index af66d02b94..477a85fbef 100644
--- a/src/wp-includes/rewrite.php
+++ b/src/wp-includes/rewrite.php
@@ -500,8 +500,21 @@ function url_to_postid( $url ) {
 	 */
 	$url = apply_filters( 'url_to_postid', $url );
 
-	$url_host      = str_replace( 'www.', '', parse_url( $url, PHP_URL_HOST ) );
-	$home_url_host = str_replace( 'www.', '', parse_url( home_url(), PHP_URL_HOST ) );
+	$url_host = parse_url( $url, PHP_URL_HOST );
+
+	if ( is_string( $url_host ) ) {
+		$url_host = str_replace( 'www.', '', $url_host );
+	} else {
+		$url_host = '';
+	}
+
+	$home_url_host = parse_url( home_url(), PHP_URL_HOST );
+
+	if ( is_string( $home_url_host ) ) {
+		$home_url_host = str_replace( 'www.', '', $home_url_host );
+	} else {
+		$home_url_host = '';
+	}
 
 	// Bail early if the URL does not belong to this site.
 	if ( $url_host && $url_host !== $home_url_host ) {
diff --git a/tests/phpunit/tests/rewrite.php b/tests/phpunit/tests/rewrite.php
index bee61dc66c..2bb7254abf 100644
--- a/tests/phpunit/tests/rewrite.php
+++ b/tests/phpunit/tests/rewrite.php
@@ -255,8 +255,17 @@ class Tests_Rewrite extends WP_UnitTestCase {
 		$this->assertSame( $grandchild_id_2, url_to_postid( get_permalink( $grandchild_id_2 ) ) );
 	}
 
-	public function test_url_to_postid_home_has_path() {
+	/**
+	 * @covers ::url_to_postid
+	 */
+	public function test_url_to_postid_url_has_only_path() {
+		$this->assertSame( 0, url_to_postid( '/example/' ) );
+	}
 
+	/**
+	 * @covers ::url_to_postid
+	 */
+	public function test_url_to_postid_home_has_only_path() {
 		update_option( 'home', home_url( '/example/' ) );
 
 		$id = self::factory()->post->create(