diff --git a/openbsc/tests/si/Makefile.am b/openbsc/tests/si/Makefile.am
index 63cf6f8..795bd30 100644
--- a/openbsc/tests/si/Makefile.am
+++ b/openbsc/tests/si/Makefile.am
@@ -1,4 +1,4 @@
-INCLUDES = $(all_includes) -I$(top_srcdir)/include
+AM_CPPFLAGS = $(all_includes) -I$(top_srcdir)/include
 AM_CFLAGS=-Wall -ggdb3 $(LIBOSMOCORE_CFLAGS) $(LIBOSMOSCCP_CFLAGS) $(COVERAGE_CFLAGS)
 
 EXTRA_DIST = si_test.ok