1 files changed, 3 insertions, 1 deletions
diff --git a/src/x11.c b/src/x11.c
index d7ac4a5..bd7d808 100644
--- a/src/x11.c
+++ b/src/x11.c
@@ -16,7 +16,9 @@
   OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */
 
-#define _POSIX_C_SOURCE 199309L
+#ifndef _POSIX_C_SOURCE
+#  define _POSIX_C_SOURCE 199309L
+#endif
 
 #include "x11.h"