diff --git a/phpBB/adm/style/acp_search_index.html b/phpBB/adm/style/acp_search_index.html
index fa09cb7991..9c2fda674a 100644
--- a/phpBB/adm/style/acp_search_index.html
+++ b/phpBB/adm/style/acp_search_index.html
@@ -10,7 +10,7 @@
 
 	{% if backend.S_STATS is not empty %}
 
-	<form id="acp_search_index_{{ backend.TYPE }}" method="post" action="{{ U_ACTION }}">
+	<form id="acp_search_index_{{ backend.TYPE|replace({'\\': '-'}) }}" method="post" action="{{ U_ACTION }}">
 
 		<fieldset class="tabulated">
 
diff --git a/phpBB/includes/acp/acp_search.php b/phpBB/includes/acp/acp_search.php
index 7eb9cf9638..48a3b103f5 100644
--- a/phpBB/includes/acp/acp_search.php
+++ b/phpBB/includes/acp/acp_search.php
@@ -21,6 +21,7 @@ use phpbb\di\service_collection;
 use phpbb\language\language;
 use phpbb\log\log;
 use phpbb\request\request;
+use phpbb\search\backend\search_backend_interface;
 use phpbb\search\search_backend_factory;
 use phpbb\search\state_helper;
 use phpbb\template\template;
@@ -322,6 +323,7 @@ class acp_search
 		$this->tpl_name = 'acp_search_index';
 		$this->page_title = 'ACP_SEARCH_INDEX';
 
+		/** @var search_backend_interface $search */
 		foreach ($this->search_backend_collection as $search)
 		{
 			$this->template->assign_block_vars('backends', [
diff --git a/tests/functional/search/base.php b/tests/functional/search/base.php
index b209c21348..c3f3f6f7dd 100644
--- a/tests/functional/search/base.php
+++ b/tests/functional/search/base.php
@@ -230,7 +230,7 @@ abstract class phpbb_functional_search_base extends phpbb_functional_test_case
 
 		// Ensure search index has been actually created
 		$crawler = self::request('GET', 'adm/index.php?i=acp_search&mode=index&sid=' . $this->sid);
-		$posts_indexed = (int) $crawler->filter('#acp_search_index_' . $search_type . ' td')->eq(1)->text();
+		$posts_indexed = (int) $crawler->filter('#acp_search_index_' . str_replace('\\', '-', $search_type) . ' td')->eq(1)->text();
 		$this->assertTrue($posts_indexed > 0);
 	}
 
@@ -267,7 +267,7 @@ abstract class phpbb_functional_search_base extends phpbb_functional_test_case
 
 		// Ensure search index has been actually removed
 		$crawler = self::request('GET', 'adm/index.php?i=acp_search&mode=index&sid=' . $this->sid);
-		$posts_indexed = (int) $crawler->filter('#acp_search_index_' . $this->search_backend . ' td')->eq(1)->text();
+		$posts_indexed = (int) $crawler->filter('#acp_search_index_' . str_replace('\\', '-', $this->search_backend) . ' td')->eq(1)->text();
 		$this->assertEquals(0, $posts_indexed);
 	}
 }