diff --git a/src/Makefile.am b/src/Makefile.am
index d4e105e..1bbcfc5 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -3,7 +3,7 @@
 # documentation before making any modification
 LIBVERSION=0:0:0
 
-INCLUDES = $(all_includes) -I$(top_srcdir)/include/asn1c
+AM_CPPFLAGS = $(all_includes) -I$(top_srcdir)/include/asn1c
 AM_CFLAGS = -fPIC -Wall $(LIBOSMOCORE_CFLAGS)
 
 lib_LTLIBRARIES = libasn1c.la