diff --git a/postconf b/postconf
index efaf510..9a9c8b0 100755
--- a/postconf
+++ b/postconf
@@ -1,6 +1,8 @@
 #!/bin/sh
 
-grep -q '^xen="true"' setup.data || exit 0
-
 export PKG_CONFIG_PATH="$(opam config var prefix)/lib/pkgconfig"
-echo "XEN_CFLAGS=\"$(pkg-config --static mirage-xen --cflags)\"" >> setup.data
+
+XEN_CFLAGS="disabled"
+grep -q '^xen="true"' setup.data && XEN_CFLAGS="$(pkg-config --static mirage-xen --cflags)"
+
+echo "XEN_CFLAGS=\"${XEN_CFLAGS}\"" >> setup.data