diff --git a/build/psalm-baseline.xml b/build/psalm-baseline.xml
index 4b122b002f23b..48a4a7a7db0b9 100644
--- a/build/psalm-baseline.xml
+++ b/build/psalm-baseline.xml
@@ -3566,6 +3566,11 @@
       <code><![CDATA[$CONFIG]]></code>
     </UndefinedVariable>
   </file>
+  <file src="lib/private/Config/UserConfig.php">
+    <RedundantCast>
+      <code><![CDATA[(string)$this->getTypedValue($userId, $app, $key, $default ? 'true' : 'false', $lazy, ValueType::BOOL)]]></code>
+    </RedundantCast>
+  </file>
   <file src="lib/private/Console/Application.php">
     <NoInterfaceProperties>
       <code><![CDATA[$this->request->server]]></code>
diff --git a/lib/private/Config/UserConfig.php b/lib/private/Config/UserConfig.php
index 12222b02ebd9f..8c551afb5cc31 100644
--- a/lib/private/Config/UserConfig.php
+++ b/lib/private/Config/UserConfig.php
@@ -705,7 +705,11 @@ public function getValueBool(
 		bool $default = false,
 		bool $lazy = false,
 	): bool {
-		$b = strtolower($this->getTypedValue($userId, $app, $key, $default ? 'true' : 'false', $lazy, ValueType::BOOL));
+		// The explicit (string) cast guards against a PHP OPcache bug where values passed
+		// by reference across function boundaries can have their type corrupted (e.g. bool
+		// returned as int). Affects PHP 8.x with OPcache enabled; fixed upstream in
+		// https://github.com/php/php-src/pull/21973. Keep until minimum PHP version is bumped.
+		$b = strtolower((string)$this->getTypedValue($userId, $app, $key, $default ? 'true' : 'false', $lazy, ValueType::BOOL));
 		return in_array($b, ['1', 'true', 'yes', 'on']);
 	}