diff --git a/vlib/v/checker/fn.v b/vlib/v/checker/fn.v
index c479bf0362..33a37bba63 100644
--- a/vlib/v/checker/fn.v
+++ b/vlib/v/checker/fn.v
@@ -1517,8 +1517,8 @@ fn (mut c Checker) method_call(mut node ast.CallExpr) ast.Type {
 		&& method_name in ['clone', 'keys', 'values', 'move', 'delete'] {
 		if left_sym.kind == .map {
 			return c.map_builtin_method_call(mut node, left_type, c.table.sym(left_type))
-		} else {
-			parent_type := (left_sym.info as ast.Alias).parent_type
+		} else if left_sym.info is ast.Alias {
+			parent_type := left_sym.info.parent_type
 			return c.map_builtin_method_call(mut node, parent_type, c.table.final_sym(left_type))
 		}
 	} else if left_sym.kind == .array && method_name in ['insert', 'prepend'] {