diff --git a/relay.go b/relay.go
index ea69eeb..a21d786 100644
--- a/relay.go
+++ b/relay.go
@@ -39,7 +39,7 @@ func (s Status) String() string {
 }
 
 type Relay struct {
-	mu sync.Mutex
+	closeMutex sync.Mutex
 
 	URL           string
 	RequestHeader http.Header // e.g. for origin header
@@ -555,8 +555,8 @@ func (r *Relay) Count(ctx context.Context, filters Filters, opts ...Subscription
 }
 
 func (r *Relay) Close() error {
-	r.mu.Lock()
-	defer r.mu.Unlock()
+	r.closeMutex.Lock()
+	defer r.closeMutex.Unlock()
 
 	if r.connectionContextCancel == nil {
 		return fmt.Errorf("relay not connected")