diff --git a/ui/vnc.c b/ui/vnc.c
index 1871422e1d..785edf3af1 100644
--- a/ui/vnc.c
+++ b/ui/vnc.c
@@ -2535,6 +2535,18 @@ void start_client_init(VncState *vs)
     vnc_read_when(vs, protocol_client_init, 1);
 }
 
+static void authentication_failed(VncState *vs)
+{
+    vnc_write_u32(vs, 1); /* Reject auth */
+    if (vs->minor >= 8) {
+        static const char err[] = "Authentication failed";
+        vnc_write_u32(vs, sizeof(err));
+        vnc_write(vs, err, sizeof(err));
+    }
+    vnc_flush(vs);
+    vnc_client_error(vs);
+}
+
 static void make_challenge(VncState *vs)
 {
     int i;
@@ -2609,14 +2621,7 @@ static int protocol_client_auth_vnc(VncState *vs, uint8_t *data, size_t len)
     return 0;
 
 reject:
-    vnc_write_u32(vs, 1); /* Reject auth */
-    if (vs->minor >= 8) {
-        static const char err[] = "Authentication failed";
-        vnc_write_u32(vs, sizeof(err));
-        vnc_write(vs, err, sizeof(err));
-    }
-    vnc_flush(vs);
-    vnc_client_error(vs);
+    authentication_failed(vs);
     qcrypto_cipher_free(cipher);
     return 0;
 }
@@ -2638,13 +2643,7 @@ static int protocol_client_auth(VncState *vs, uint8_t *data, size_t len)
      * must pick the one we sent. Verify this */
     if (data[0] != vs->auth) { /* Reject auth */
        trace_vnc_auth_reject(vs, vs->auth, (int)data[0]);
-       vnc_write_u32(vs, 1);
-       if (vs->minor >= 8) {
-           static const char err[] = "Authentication failed";
-           vnc_write_u32(vs, sizeof(err));
-           vnc_write(vs, err, sizeof(err));
-       }
-       vnc_client_error(vs);
+       authentication_failed(vs);
     } else { /* Accept requested auth */
        trace_vnc_auth_start(vs, vs->auth);
        switch (vs->auth) {
@@ -2673,13 +2672,7 @@ static int protocol_client_auth(VncState *vs, uint8_t *data, size_t len)
 
        default: /* Should not be possible, but just in case */
            trace_vnc_auth_fail(vs, vs->auth, "Unhandled auth method", "");
-           vnc_write_u8(vs, 1);
-           if (vs->minor >= 8) {
-               static const char err[] = "Authentication failed";
-               vnc_write_u32(vs, sizeof(err));
-               vnc_write(vs, err, sizeof(err));
-           }
-           vnc_client_error(vs);
+           authentication_failed(vs);
        }
     }
     return 0;