diff --git a/cmd/stdiscosrv/querysrv.go b/cmd/stdiscosrv/querysrv.go
index 54dbd6e53..1bd8739fb 100644
--- a/cmd/stdiscosrv/querysrv.go
+++ b/cmd/stdiscosrv/querysrv.go
@@ -62,6 +62,10 @@ func (i requestID) String() string {
 	return fmt.Sprintf("%016x", int64(i))
 }
 
+type contextKey int
+
+const idKey contextKey = iota
+
 func negCacheFor(lastSeen time.Time) int {
 	since := time.Since(lastSeen).Seconds()
 	if since >= maxDeviceAge {
@@ -132,7 +136,7 @@ var topCtx = context.Background()
 
 func (s *querysrv) handler(w http.ResponseWriter, req *http.Request) {
 	reqID := requestID(rand.Int63())
-	ctx := context.WithValue(topCtx, "id", reqID)
+	ctx := context.WithValue(topCtx, idKey, reqID)
 
 	if debug {
 		log.Println(reqID, req.Method, req.URL)
@@ -186,7 +190,7 @@ func (s *querysrv) handler(w http.ResponseWriter, req *http.Request) {
 }
 
 func (s *querysrv) handleGET(ctx context.Context, w http.ResponseWriter, req *http.Request) {
-	reqID := ctx.Value("id").(requestID)
+	reqID := ctx.Value(idKey).(requestID)
 
 	deviceID, err := protocol.DeviceIDFromString(req.URL.Query().Get("device"))
 	if err != nil {
@@ -238,7 +242,7 @@ func (s *querysrv) handleGET(ctx context.Context, w http.ResponseWriter, req *ht
 }
 
 func (s *querysrv) handlePOST(ctx context.Context, remoteIP net.IP, w http.ResponseWriter, req *http.Request) {
-	reqID := ctx.Value("id").(requestID)
+	reqID := ctx.Value(idKey).(requestID)
 
 	rawCert := certificateBytes(req)
 	if rawCert == nil {
@@ -299,7 +303,7 @@ func (s *querysrv) Stop() {
 }
 
 func (s *querysrv) handleAnnounce(ctx context.Context, remote net.IP, deviceID protocol.DeviceID, addresses []string) (userErr, internalErr error) {
-	reqID := ctx.Value("id").(requestID)
+	reqID := ctx.Value(idKey).(requestID)
 
 	tx, err := s.db.Begin()
 	if err != nil {
@@ -383,7 +387,7 @@ func (s *querysrv) limit(remote net.IP) bool {
 }
 
 func (s *querysrv) updateDevice(ctx context.Context, tx *sql.Tx, device protocol.DeviceID) error {
-	reqID := ctx.Value("id").(requestID)
+	reqID := ctx.Value(idKey).(requestID)
 	t0 := time.Now()
 	res, err := tx.Stmt(s.prep["updateDevice"]).Exec(device.String())
 	if err != nil {