diff --git a/library.c b/library.c
index af887d8b..440ec9e3 100644
--- a/library.c
+++ b/library.c
@@ -582,7 +582,7 @@ void openconnect_set_stats_handler(struct openconnect_info *vpninfo,
 /* Set up a traditional OS-based tunnel device, optionally specified in 'ifname'. */
 int openconnect_setup_tun_device(struct openconnect_info *vpninfo, char *vpnc_script, char *ifname)
 {
-	int tun_fd;
+	intptr_t tun_fd;
 
 	vpninfo->vpnc_script = vpnc_script;
 	vpninfo->ifname = ifname;
diff --git a/openconnect-internal.h b/openconnect-internal.h
index 6379e001..004cb38b 100644
--- a/openconnect-internal.h
+++ b/openconnect-internal.h
@@ -455,7 +455,7 @@ int script_config_tun(struct openconnect_info *vpninfo, const char *reason);
 void os_shutdown_tun(struct openconnect_info *vpninfo);
 int os_read_tun(struct openconnect_info *vpninfo, struct pkt *pkt, int new_pkt);
 int os_write_tun(struct openconnect_info *vpninfo, struct pkt *pkt);
-int os_setup_tun(struct openconnect_info *vpninfo);
+intptr_t os_setup_tun(struct openconnect_info *vpninfo);
 
 /* dtls.c */
 unsigned char unhex(const char *data);
diff --git a/openconnect.h b/openconnect.h
index 714269e8..08e54940 100644
--- a/openconnect.h
+++ b/openconnect.h
@@ -336,9 +336,13 @@ int openconnect_setup_tun_device(struct openconnect_info *vpninfo, char *vpnc_sc
 /* Pass traffic to a script program (no tun device). */
 int openconnect_setup_tun_script(struct openconnect_info *vpninfo, char *tun_script);
 
+#ifdef _WIN32
+/* Caller will provide an overlap-capable handle for the tunnel traffic. */
+int openconnect_setup_tun_fd(struct openconnect_info *vpninfo, intptr_t tun_fd);
+#else
 /* Caller will provide a file descriptor for the tunnel traffic. */
 int openconnect_setup_tun_fd(struct openconnect_info *vpninfo, int tun_fd);
-
+#endif
 /* Optional call to enable DTLS on the connection. */
 int openconnect_setup_dtls(struct openconnect_info *vpninfo, int dtls_attempt_period);
 
diff --git a/tun-win32.c b/tun-win32.c
index 1fcf0fcb..d99005bf 100644
--- a/tun-win32.c
+++ b/tun-win32.c
@@ -192,19 +192,12 @@ static intptr_t open_tun(struct openconnect_info *vpninfo, char *guid, char *nam
 	if (!vpninfo->ifname)
 		vpninfo->ifname = strdup(name);
 
-	vpninfo->tun_fh = tun_fh;
-	vpninfo->tun_rd_overlap.hEvent = CreateEvent(NULL, FALSE, FALSE, NULL);
-	monitor_read_fd(vpninfo, tun);
-
-	return 1;
+	return (intptr_t)tun_fh;
 }
 
-int os_setup_tun(struct openconnect_info *vpninfo)
+intptr_t os_setup_tun(struct openconnect_info *vpninfo)
 {
-	if (search_taps(vpninfo, open_tun, 0) != 1)
-		return -1;
-
-	return 0;
+	return search_taps(vpninfo, open_tun, 0);
 }
 
 int os_read_tun(struct openconnect_info *vpninfo, struct pkt *pkt, int new_pkt)
@@ -277,7 +270,11 @@ void os_shutdown_tun(struct openconnect_info *vpninfo)
 	vpninfo->tun_rd_overlap.hEvent = NULL;
 }
 
-int openconnect_setup_tun_fd(struct openconnect_info *vpninfo, int tun_fd)
+int openconnect_setup_tun_fd(struct openconnect_info *vpninfo, intptr_t tun_fd)
 {
+	vpninfo->tun_fh = (HANDLE)tun_fd;
+	vpninfo->tun_rd_overlap.hEvent = CreateEvent(NULL, FALSE, FALSE, NULL);
+	monitor_read_fd(vpninfo, tun);
+
 	return 0;
 }
diff --git a/tun.c b/tun.c
index 7d676cce..18563490 100644
--- a/tun.c
+++ b/tun.c
@@ -169,7 +169,7 @@ static int bsd_open_tun(char *tun_name)
 #define bsd_open_tun(tun_name) open(tun_name, O_RDWR)
 #endif
 
-int os_setup_tun(struct openconnect_info *vpninfo)
+intptr_t os_setup_tun(struct openconnect_info *vpninfo)
 {
 	int tun_fd = -1;
 #ifdef IFF_TUN /* Linux */