diff --git a/src/parser.c b/src/parser.c
index cd92951..555c5e7 100644
--- a/src/parser.c
+++ b/src/parser.c
@@ -1445,7 +1445,7 @@ readtoken1_parsesub(char *out, int c, char *eofmark, int flags)
 			default:
 				p = strchr(types, c);
 				if (p == NULL)
-					break;
+					goto badsub;
 				subtype |= p - types + VSNORMAL;
 				break;
 			case '%':