diff --git a/src/c/tcp.d b/src/c/tcp.d
index 59794554b..c914aa992 100644
--- a/src/c/tcp.d
+++ b/src/c/tcp.d
@@ -28,6 +28,7 @@ extern int errno;
 #include <sys/socket.h>
 #include <sys/un.h>
 #include <netinet/in.h>
+#include <netinet/tcp.h>
 #include <arpa/inet.h>
 #include <netdb.h>
 #include <unistd.h>