diff --git a/skeletons/converter-example.c b/skeletons/converter-example.c
index a1dc37b7..c90c39d6 100644
--- a/skeletons/converter-example.c
+++ b/skeletons/converter-example.c
@@ -27,6 +27,7 @@
 #ifndef NO_ASN_PDU
 #ifndef PDU
 #error Define -DPDU to compile this sample converter.
+#error `asn1c -pdu=...` adds it automatically.
 #endif
 #ifdef    ASN_PDU_COLLECTION        /* Generated by asn1c: -pdu=... */
 extern asn_TYPE_descriptor_t *asn_pdu_collection[];