diff --git a/Sources/User.php b/Sources/User.php
index f8208a36ad..60fdb8d431 100644
--- a/Sources/User.php
+++ b/Sources/User.php
@@ -4513,7 +4513,7 @@ protected function setLanguage(): void
 		$languages = Lang::get();
 
 		// Change was requested in URL parameters.
-		if (!empty($_GET['language']) && isset($languages[strtr($_GET['language'], './\\:', '____')])) {
+		if (!empty($_GET['language']) && \is_string($_GET['language']) && isset($languages[strtr($_GET['language'], './\\:', '____')])) {
 			$this->language = strtr($_GET['language'], './\\:', '____');
 
 			// Make it permanent for members.