diff --git a/lam/lib/types.inc b/lam/lib/types.inc
index f84a740d7..2decfd87b 100644
--- a/lam/lib/types.inc
+++ b/lam/lib/types.inc
@@ -106,7 +106,7 @@ class ConfiguredType {
 
 	private string $id;
 
-	private $suffix;
+	private string $suffix;
 
 	private $attributes;