diff --git a/lib/Makefile.am b/lib/Makefile.am
index 082408c..c2815c4 100644
--- a/lib/Makefile.am
+++ b/lib/Makefile.am
@@ -1,6 +1,6 @@
 # -*- Makefile -*-
 
-AM_CFLAGS  = -Wall -I${top_srcdir}/include -D_GNU_SOURCE -DSYSCONFDIR=\"$(sysconfdir)/libnl\"
+AM_CPPFLAGS  = -Wall -I${top_srcdir}/include -D_GNU_SOURCE -DSYSCONFDIR=\"$(sysconfdir)/libnl\"
 
 lib_LTLIBRARIES = \
 	libnl.la libnl-genl.la libnl-route.la libnl-nf.la
diff --git a/src/Makefile.am b/src/Makefile.am
index 4e2b57c..d72284d 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -2,7 +2,7 @@
 
 SUBDIRS = lib
 
-AM_CFLAGS  = -Wall -I${top_srcdir}/include -D_GNU_SOURCE
+AM_CPPFLAGS  = -Wall -I${top_srcdir}/include -D_GNU_SOURCE
 AM_LDFLAGS = -L${top_builddir}/lib -L${top_builddir}/src/lib -lnl-cli
 
 noinst_PROGRAMS = \