diff --git a/openbsc/src/libgb/Makefile.am b/openbsc/src/libgb/Makefile.am
index eafbc34..1592431 100644
--- a/openbsc/src/libgb/Makefile.am
+++ b/openbsc/src/libgb/Makefile.am
@@ -1,4 +1,4 @@
-INCLUDES = $(all_includes) -I$(top_srcdir)/include -I$(top_builddir)
+AM_CPPFLAGS = $(all_includes) -I$(top_srcdir)/include -I$(top_builddir)
 AM_CFLAGS=-Wall -fno-strict-aliasing $(LIBOSMOCORE_CFLAGS) \
 	$(LIBOSMOVTY_CFLAGS) $(LIBOSMOABIS_CFLAGS) $(COVERAGE_CFLAGS)