diff --git a/lib/quicly.c b/lib/quicly.c
index e3cd4d77..cd862f6e 100644
--- a/lib/quicly.c
+++ b/lib/quicly.c
@@ -21,6 +21,7 @@
  */
 #include <assert.h>
 #include <inttypes.h>
+#include <sys/types.h>
 #include <netinet/in.h>
 #include <netinet/ip.h>
 #include <pthread.h>