diff --git a/Makefile.am b/Makefile.am
index b3620bdeb..5e6747e6d 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -1,7 +1,7 @@
 ACLOCAL_AMFLAGS = -I m4
 AUTOMAKE_OPTIONS = foreign 1.10 dist-bzip2 subdir-objects
 
-AM_CPPFLAGS = -I$(srcdir)/src $(GLIB_CFLAGS)
+AM_CPPFLAGS += -I$(srcdir)/src $(GLIB_CFLAGS)
 
 AM_CPPFLAGS += -DSYSTEM_CONFIG_FILE_LOCATION='"$(sysconfdir)/mpd.conf"'
 
diff --git a/configure.ac b/configure.ac
index 559284332..24b9a857d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -37,7 +37,9 @@ PKG_PROG_PKG_CONFIG
 dnl ---------------------------------------------------------------------------
 dnl Declare Variables
 dnl ---------------------------------------------------------------------------
+AC_SUBST(AM_CPPFLAGS,"")
 AC_SUBST(AM_CFLAGS,"")
+AC_SUBST(AM_CXXFLAGS,"")
 
 AC_SUBST(MPD_LIBS)
 AC_SUBST(MPD_CFLAGS)