Turn on subdir-objects automake option.
diff --git a/configure.ac b/configure.ac
index c0507a6..01b6109 100644
--- a/configure.ac
+++ b/configure.ac
@@ -11,7 +11,7 @@
 AC_CONFIG_AUX_DIR(config)
 AC_CONFIG_HEADER([config.h])
 
-AM_INIT_AUTOMAKE([1.9.6 foreign])
+AM_INIT_AUTOMAKE([1.9.6 foreign subdir-objects])
 AM_MAINTAINER_MODE
 
 #