diff --git a/src/hnbap/Makefile.am b/src/hnbap/Makefile.am
index 131bef1..8a2c56a 100644
--- a/src/hnbap/Makefile.am
+++ b/src/hnbap/Makefile.am
@@ -234,6 +234,8 @@
 
 AM_CFLAGS = -I$(top_srcdir)/include $(ASN1C_CFLAGS) $(OSMOCORE_CFLAGS)
 
+HNBAP_ASN1 = $(top_srcdir)/asn1/hnbap
+
 noinst_LIBRARIES=libosmo-asn1-hnbap.a
 libosmo_asn1_hnbap_a_SOURCES=$(ASN_MODULE_SOURCES)
 libosmo_asn1_hnbap_a_LIBADD=$(ASN1C_LDADD)
@@ -241,7 +243,7 @@
 regen: regenerate-from-asn1-source
 
 regenerate-from-asn1-source:
-	asn1c -gen-PER -fnative-types $(top_srcdir)/asn1/hnbap/HNBAP-CommonDataTypes.asn $(top_srcdir)/asn1/hnbap/HNBAP-Constants.asn $(top_srcdir)/asn1/hnbap/HNBAP-IEs.asn $(top_srcdir)/asn1/hnbap/HNBAP-PDU.asn
+	asn1c -gen-PER -fnative-types $(HNBAP_ASN1)/HNBAP-CommonDataTypes.asn $(HNBAP_ASN1)/HNBAP-Constants.asn $(HNBAP_ASN1)/HNBAP-IEs.asn $(HNBAP_ASN1)/HNBAP-PDU.asn
 #	remove the local copy of the runtime code
 	-rm ANY.* BOOLEAN.* INTEGER.* NativeEnumerated.* NativeInteger.* OBJECT_IDENTIFIER.* asn_* OCTET_STRING.* converter-sample.c per_* xer_* constr* der_* ber_* BIT_STRING.*
 #	change include style to `#include <dir/foo.h>'