better parsing information object class sets
diff --git a/libasn1parser/asn1p_oid.h b/libasn1parser/asn1p_oid.h
index 489a3c5..1b7ba52 100644
--- a/libasn1parser/asn1p_oid.h
+++ b/libasn1parser/asn1p_oid.h
@@ -61,7 +61,7 @@
  *	0: The specified OIDs are equal.
  *	-1 or 1 otherwise.
  */
-int asn1p_oid_compare(asn1p_oid_t *a, asn1p_oid_t *b);
+int asn1p_oid_compare(const asn1p_oid_t *a, const asn1p_oid_t *b);
 
 
 #endif	/* ASN1_PARSER_OID_H */