diff --git a/lua/wincent/commandt/lib/xstrdup.c b/lua/wincent/commandt/lib/xstrdup.c
index 4afe7ed4..727bd514 100644
--- a/lua/wincent/commandt/lib/xstrdup.c
+++ b/lua/wincent/commandt/lib/xstrdup.c
@@ -5,6 +5,8 @@
 
 #include "xstrdup.h"
 
+#define _POSIX_C_SOURCE 200809L /* needed in order to see strdup() */
+
 #include <stddef.h> /* for NULL */
 #include <stdlib.h> /* for abort() */
 #include <string.h> /* for strdup() */