diff --git a/tcpip.cc b/tcpip.cc
index 58c2f9b1c..5d4583fae 100644
--- a/tcpip.cc
+++ b/tcpip.cc
@@ -167,7 +167,7 @@ void set_ipoptions(int sd, void *opts, size_t optslen)
 	if (sd == -1)
 		return;
 
-	setsockopt(sd, IPPROTO_IP, IP_OPTIONS, opts, optslen);
+	setsockopt(sd, IPPROTO_IP, IP_OPTIONS, (const char *) opts, optslen);
 #endif
 }