diff --git a/src/ZVal.cc b/src/ZVal.cc
index 119d8c3f2e..0adaa70941 100644
--- a/src/ZVal.cc
+++ b/src/ZVal.cc
@@ -263,8 +263,9 @@ ValPtr ZVal::ToVal(const TypePtr& t) const
 	case TYPE_TIMER:
 	case TYPE_UNION:
 	case TYPE_VOID:
+	default:
 		v = nullptr;
-		reporter->InternalError("bad ret type return tag");
+		reporter->InternalError("bad type in ZVal::ToVal: %s", type_name(t->Tag()));
 	}
 
 	if ( v )