diff --git a/libavformat/os_support.c b/libavformat/os_support.c
index d9b6c1ed69..4b8e16d681 100644
--- a/libavformat/os_support.c
+++ b/libavformat/os_support.c
@@ -22,6 +22,7 @@
 
 /* needed by inet_aton() */
 #define _SVID_SOURCE
+#define _DARWIN_C_SOURCE
 
 #include "config.h"
 #include "avformat.h"