diff --git a/libavformat/os_support.c b/libavformat/os_support.c
index e8f063aaf87c812813676c782dec76f8a7852453..f9d6eeaf90b3c1470593fb2eab3078aec72513fc 100644
--- a/libavformat/os_support.c
+++ b/libavformat/os_support.c
@@ -21,6 +21,7 @@
  */
 
 /* needed by inet_aton() */
+#define _DEFAULT_SOURCE
 #define _SVID_SOURCE
 
 #include "config.h"