diff --git a/src/c/package.d b/src/c/package.d
index 431388ffa..60c6d6cde 100644
--- a/src/c/package.d
+++ b/src/c/package.d
@@ -15,9 +15,6 @@
     See file '../Copyright' for full details.
 */
 
-#ifndef __sun__ /* See unixint.d for the reason of this */
-#define _XOPEN_SOURCE 600	/* For pthread mutex attributes */
-#endif
 #include <ecl/ecl.h>
 #include <ecl/internal.h>
 #include <ecl/ecl-inl.h>