diff --git src/bp-groups/bp-groups-functions.php src/bp-groups/bp-groups-functions.php
index e789119c7..4e3183e09 100644
--- src/bp-groups/bp-groups-functions.php
+++ src/bp-groups/bp-groups-functions.php
@@ -3673,8 +3673,8 @@ function bp_init_group_extensions() {
 	foreach ( array_keys( $registered_group_extensions ) as $group_extension_class ) {
 		$extension = new $group_extension_class;
 
-		add_action( 'bp_actions', array( &$extension, '_register' ), 8 );
-		add_action( 'admin_init', array( &$extension, '_register' ) );
+		add_action( 'bp_actions', array( $extension, '_register' ), 8 );
+		add_action( 'admin_init', array( $extension, '_register' ) );
 	}
 }
 add_action( 'bp_init', 'bp_init_group_extensions', 11 );
diff --git tests/phpunit/testcases/groups/class-bp-group-extension.php tests/phpunit/testcases/groups/class-bp-group-extension.php
index 9e1e8b8b0..e640c8793 100644
--- tests/phpunit/testcases/groups/class-bp-group-extension.php
+++ tests/phpunit/testcases/groups/class-bp-group-extension.php
@@ -887,4 +887,39 @@ class BP_Tests_Group_Extension_TestCases extends BP_UnitTestCase {
 
 		$this->assertFalse( $content === 'Widget Displayed' );
 	}
+
+	/**
+	 * @ticket BP8558
+	 */
+	public function test_adding_multiple_extension_classes() {
+		$old_options_nav = buddypress()->bp_options_nav;
+
+		$g = self::factory()->group->create();
+		$g_obj = groups_get_group( $g );
+
+		$e = new BPTest_Group_Extension_Enable_Nav_Item_True();
+		$e_slug = 'bptest_group_extension_enable_nav_item_true';
+		$e_class_name = get_class( $e );
+		$f = new BPTest_Group_Extension_Access_Anyone();
+		$f_slug = 'bptest_group_extension_access_anyone';
+		$f_class_name = get_class( $f );
+
+		bp_register_group_extension( $e_class_name );
+		bp_register_group_extension( $f_class_name );
+
+		$this->go_to( bp_get_group_permalink( $g_obj ) );
+		$nav = buddypress()->groups->nav->get_secondary( array(
+			'parent_slug' => $g_obj->slug ,
+		) );
+
+		$slugs = array();
+		foreach ( $nav as $priority => $nav_obj ) {
+			$slugs[] = $nav_obj->slug;
+		}
+
+		$this->assertTrue( in_array( $e_slug, $slugs, true ) && in_array( $f_slug, $slugs, true ) );
+
+		// Clean up
+		buddypress()->bp_options_nav = $old_options_nav;
+	}
 }