diff --git a/lib/config/base-type.conf b/lib/config/base-type.conf
index 4912f7a40..b9b53d0e3 100644
--- a/lib/config/base-type.conf
+++ b/lib/config/base-type.conf
@@ -29,7 +29,9 @@ type DynamicObject {
 
 	%attribute dictionary "methods",
 
-	%attribute any "custom::*"
+	%attribute dictionary "custom" {
+		%attribute string "*"
+	}
 }
 
 type Logger {