diff --git a/simgear/xml/Makefile.am b/simgear/xml/Makefile.am
index 613ef545..035d4e7b 100644
--- a/simgear/xml/Makefile.am
+++ b/simgear/xml/Makefile.am
@@ -1,3 +1,5 @@
+includedir = @includedir@/xml
+
 if HAVE_ZLIB
 ZLIB_INCL =
 else