diff --git a/openbsc/tests/v42bis/v42bis_test.c b/openbsc/tests/v42bis/v42bis_test.c
index 4e05514..7e90785 100644
--- a/openbsc/tests/v42bis/v42bis_test.c
+++ b/openbsc/tests/v42bis/v42bis_test.c
@@ -318,6 +318,7 @@
 	len = strlen(uncompr_packets[packet_id]);
 	testvec = talloc_zero_size(ctx, len);
 	len = osmo_hexparse(uncompr_packets[packet_id], testvec, len);
+	OSMO_ASSERT(len > 0);
 	v42bis(ctx, V42BIS_COMPRESSION_MODE_DYNAMIC, testvec, len);
 	v42bis(ctx, V42BIS_COMPRESSION_MODE_ALWAYS, testvec, len);
 	v42bis(ctx, V42BIS_COMPRESSION_MODE_NEVER, testvec, len);