--- config.m4.old	2014-02-26 14:17:31.000000000 +0100
+++ config.m4	2014-02-26 14:22:36.000000000 +0100
@@ -148,4 +148,13 @@
     -L$MONGO_SASL_DIR/$PHP_LIBDIR
   ])
   PHP_SUBST(MONGO_SHARED_LIBADD)
+
+fi
+
+AC_MSG_CHECKING(for JSON)
+if test -f "$phpincludedir/ext/json/php_json.h"; then
+  AC_DEFINE(HAVE_JSON, 1, [JSON support])
+  AC_MSG_RESULT(Yes)
+else
+  AC_MSG_RESULT(Missing json or jsonc extension)
 fi