diff --git a/src/wp-admin/includes/class-wp-screen.php b/src/wp-admin/includes/class-wp-screen.php
index 25373191ba..c7b35a49ad 100644
--- a/src/wp-admin/includes/class-wp-screen.php
+++ b/src/wp-admin/includes/class-wp-screen.php
@@ -530,7 +530,7 @@ final class WP_Screen {
 			}
 		}
 
-		sort( $priorities );
+		ksort( $priorities );
 
 		$sorted = array();
 		foreach ( $priorities as $list ) {
diff --git a/tests/phpunit/tests/admin/includesScreen.php b/tests/phpunit/tests/admin/includesScreen.php
index 65603e315d..1805d2db03 100644
--- a/tests/phpunit/tests/admin/includesScreen.php
+++ b/tests/phpunit/tests/admin/includesScreen.php
@@ -2,6 +2,7 @@
 
 /**
  * @group admin
+ * @group adminScreen
  */
 class Tests_Admin_includesScreen extends WP_UnitTestCase {
 	var $core_screens = array(
@@ -187,54 +188,90 @@ class Tests_Admin_includesScreen extends WP_UnitTestCase {
 	function test_help_tabs_priority() {
 		$tab_1      = rand_str();
 		$tab_1_args = array(
-			'id'       => $tab_1,
 			'title'    => 'Help!',
+			'id'       => $tab_1,
 			'content'  => 'Some content',
 			'callback' => false,
-			'priority' => 11,
+			'priority' => 10,
 		);
 
 		$tab_2      = rand_str();
 		$tab_2_args = array(
-			'id'       => $tab_2,
 			'title'    => 'Help!',
+			'id'       => $tab_2,
 			'content'  => 'Some content',
 			'callback' => false,
-			'priority' => 9,
+			'priority' => 2,
+		);
+		$tab_3      = rand_str();
+		$tab_3_args = array(
+			'title'    => 'help!',
+			'id'       => $tab_3,
+			'content'  => 'some content',
+			'callback' => false,
+			'priority' => 40,
+		);
+		$tab_4      = rand_str();
+		$tab_4_args = array(
+			'title'    => 'help!',
+			'id'       => $tab_4,
+			'content'  => 'some content',
+			'callback' => false,
+			// Don't include a priority
 		);
 
 		$screen = get_current_screen();
 
-		// Add help tabs.
+		// add help tabs.
 
 		$screen->add_help_tab( $tab_1_args );
-		$this->assertEquals( $screen->get_help_tab( $tab_1 ), $tab_1_args );
+		$this->assertequals( $screen->get_help_tab( $tab_1 ), $tab_1_args );
 
 		$screen->add_help_tab( $tab_2_args );
 		$this->assertEquals( $screen->get_help_tab( $tab_2 ), $tab_2_args );
 
+		$screen->add_help_tab( $tab_3_args );
+		$this->assertEquals( $screen->get_help_tab( $tab_3 ), $tab_3_args );
+
+		$screen->add_help_tab( $tab_4_args );
+		// Priority is added with the default for future calls
+		$tab_4_args[ 'priority' ] = 10;
+		$this->assertEquals( $screen->get_help_tab( $tab_4 ), $tab_4_args );
+
 		$tabs = $screen->get_help_tabs();
-		$this->assertEquals( 2, count( $tabs ) );
+		$this->assertEquals( 4, count( $tabs ) );
 		$this->assertArrayHasKey( $tab_1, $tabs );
 		$this->assertArrayHasKey( $tab_2, $tabs );
+		$this->assertArrayHasKey( $tab_3, $tabs );
+		$this->assertArrayHasKey( $tab_4, $tabs );
 
 		// Test priority order.
 
-		$this->assertEquals( $tabs, array(
+		$this->assertSame( array(
 			$tab_2 => $tab_2_args,
 			$tab_1 => $tab_1_args,
-		) );
+			$tab_4 => $tab_4_args,
+			$tab_3 => $tab_3_args,
+		), $tabs );
 
 		$screen->remove_help_tab( $tab_1 );
 		$this->assertNull( $screen->get_help_tab( $tab_1 ) );
-		$this->assertEquals( 1, count( $screen->get_help_tabs() ) );
+		$this->assertSame( 3, count( $screen->get_help_tabs() ) );
 
 		$screen->remove_help_tab( $tab_2 );
 		$this->assertNull( $screen->get_help_tab( $tab_2 ) );
-		$this->assertEquals( 0, count( $screen->get_help_tabs() ) );
+		$this->assertSame( 2, count( $screen->get_help_tabs() ) );
+
+		$screen->remove_help_tab( $tab_3 );
+		$this->assertNull( $screen->get_help_tab( $tab_3 ) );
+		$this->assertSame( 1, count( $screen->get_help_tabs() ) );
+
+		$screen->remove_help_tab( $tab_4 );
+		$this->assertNull( $screen->get_help_tab( $tab_4 ) );
+		$this->assertSame( 0, count( $screen->get_help_tabs() ) );
 
 		$screen->remove_help_tabs();
-		$this->assertEquals( $screen->get_help_tabs(), array() );
+		$this->assertEquals( array(), $screen->get_help_tabs() );
 	}
 
 	/**