diff --git a/lib/gks/gksforbnd.c b/lib/gks/gksforbnd.c
index 85e9e4a4e..1fd811e90 100644
--- a/lib/gks/gksforbnd.c
+++ b/lib/gks/gksforbnd.c
@@ -1,5 +1,7 @@
 #ifdef __unix__
+#ifndef __FreeBSD__
 #define _POSIX_C_SOURCE 200112L
+#endif
 #define _XOPEN_SOURCE
 #endif