diff --git a/tests/db/Makefile.am b/tests/db/Makefile.am
index ece34d3..b07460e 100644
--- a/tests/db/Makefile.am
+++ b/tests/db/Makefile.am
@@ -1,7 +1,10 @@
-AM_CFLAGS = \
+AM_CPPFLAGS = \
 	$(all_includes) \
 	-I$(top_srcdir)/include \
 	-I$(top_builddir)/include \
+	$(NULL)
+
+AM_CFLAGS = \
 	-Wall \
 	-ggdb3 \
 	$(LIBOSMOCORE_CFLAGS) \