diff --git a/Makefile.am b/Makefile.am
index 11a4460..7d552ef 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -1,6 +1,6 @@
 ACLOCAL_AMFLAGS = -I m4
 
-AM_CFLAGS = -I src
+AM_CPPFLAGS = -I src
 
 SUBDIRS = po po4a src/pam_panic src/pam_panic_pw