diff --git a/doc/reference/Makefile.am b/doc/reference/Makefile.am
index 13ae307..ac4cb93 100644
--- a/doc/reference/Makefile.am
+++ b/doc/reference/Makefile.am
@@ -19,7 +19,9 @@ CFILE_GLOB =					\
 
 AM_CPPFLAGS =					\
 	-I$(top_builddir)			\
-	-I$(top_srcdir)				\
+	-I$(top_srcdir)
+
+AM_CFLAGS =					\
 	$(GLIB_CFLAGS)
 
 GTKDOC_LIBS =					\