--- a/libjaylink/discovery_tcp.c
+++ b/libjaylink/discovery_tcp.c
@@ -228,7 +228,11 @@ static struct jaylink_device *probe_device(struct jaylink_context *ctx,
 JAYLINK_PRIV int discovery_tcp_scan(struct jaylink_context *ctx)
 {
 	int ret;
+#ifdef _WIN32
+	SOCKET sock;
+#else
 	int sock;
+#endif
 	int opt_value;
 	fd_set rfds;
 	struct sockaddr_in addr;
@@ -241,7 +245,7 @@ JAYLINK_PRIV int discovery_tcp_scan(struct jaylink_context *ctx)
 
 	sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
 
-	if (sock < 0) {
+	if (sock == INVALID_SOCKET) {
 		log_err(ctx, "Failed to create discovery socket.");
 		return JAYLINK_ERR;
 	}
--- a/libjaylink/transport_tcp.c
+++ b/libjaylink/transport_tcp.c
@@ -231,7 +231,11 @@ JAYLINK_PRIV int transport_tcp_open(struct jaylink_device_handle *devh)
 	struct jaylink_device *dev;
 	struct addrinfo hints;
 	struct addrinfo *info;
+#ifdef _WIN32
+	SOCKET sock;
+#else
 	int sock;
+#endif
 
 	dev = devh->dev;
 	ctx = dev->ctx;
@@ -264,7 +268,7 @@ JAYLINK_PRIV int transport_tcp_open(struct jaylink_device_handle *devh)
 	for (struct addrinfo *rp = info; rp != NULL; rp = rp->ai_next) {
 		sock = socket(rp->ai_family, rp->ai_socktype, rp->ai_protocol);
 
-		if (sock < 0)
+		if (sock == INVALID_SOCKET)
 			continue;
 
 		if (!connect(sock, info->ai_addr, info->ai_addrlen))
@@ -276,7 +280,7 @@ JAYLINK_PRIV int transport_tcp_open(struct jaylink_device_handle *devh)
 
 	freeaddrinfo(info);
 
-	if (sock < 0) {
+	if (sock == INVALID_SOCKET) {
 		log_err(ctx, "Failed to open device.");
 		cleanup_handle(devh);
 		return JAYLINK_ERR;