diff --git a/src/vim9instr.c b/src/vim9instr.c
index 8ee9e7c..3547d42 100644
--- a/src/vim9instr.c
+++ b/src/vim9instr.c
@@ -240,6 +240,7 @@
 	case VAR_INSTR:
 	case VAR_CLASS:
 	case VAR_OBJECT:
+	case VAR_TYPEALIAS:
 			 to_string_error(type->tt_type);
 			 return FAIL;
     }