diff --git a/src/wp-includes/taxonomy.php b/src/wp-includes/taxonomy.php
index f161a71818..91ac0cdb24 100644
--- a/src/wp-includes/taxonomy.php
+++ b/src/wp-includes/taxonomy.php
@@ -408,7 +408,7 @@ function is_taxonomy_hierarchical( $taxonomy ) {
  *     @type bool          $_builtin              This taxonomy is a "built-in" taxonomy. INTERNAL USE ONLY!
  *                                                Default false.
  * }
- * @return void|WP_Error Void on success, WP_Error object on failure.
+ * @return WP_Taxonomy|WP_Error The registered taxonomy object on success, WP_Error object on failure.
  */
 function register_taxonomy( $taxonomy, $object_type, $args = array() ) {
 	global $wp_taxonomies;
@@ -441,6 +441,8 @@ function register_taxonomy( $taxonomy, $object_type, $args = array() ) {
 	 * @param array        $args        Array of taxonomy registration arguments.
 	 */
 	do_action( 'registered_taxonomy', $taxonomy, $object_type, (array) $taxonomy_object );
+
+	return $taxonomy_object;
 }
 
 /**
diff --git a/tests/phpunit/tests/post/types.php b/tests/phpunit/tests/post/types.php
index 2e5313c368..9632b8d472 100644
--- a/tests/phpunit/tests/post/types.php
+++ b/tests/phpunit/tests/post/types.php
@@ -39,6 +39,13 @@ class Tests_Post_Types extends WP_UnitTestCase {
 		_unregister_post_type( 'foo' );
 	}
 
+	/**
+	 * @ticket 48558
+	 */
+	function test_register_post_type_return_value() {
+		$this->assertInstanceOf( 'WP_Post_Type', register_post_type( 'foo' ) );
+	}
+
 	/**
 	 * @ticket 31134
 	 *
diff --git a/tests/phpunit/tests/taxonomy.php b/tests/phpunit/tests/taxonomy.php
index 62f098fe0a..adf61e76fc 100644
--- a/tests/phpunit/tests/taxonomy.php
+++ b/tests/phpunit/tests/taxonomy.php
@@ -169,6 +169,13 @@ class Tests_Taxonomy extends WP_UnitTestCase {
 		unset( $GLOBALS['wp_taxonomies'][ $tax ] );
 	}
 
+	/**
+	 * @ticket 48558
+	 */
+	function test_register_taxonomy_return_value() {
+		$this->assertInstanceOf( 'WP_Taxonomy', register_taxonomy( 'foo', 'post' ) );
+	}
+
 	/**
 	 * @ticket 21593
 	 *