diff --git a/engine.go b/engine.go
index 4b672a6..632707d 100644
--- a/engine.go
+++ b/engine.go
@@ -436,10 +436,13 @@ func (e *Engine) Unsubscribe(o chan Reply, id int64) {
 			return
 		}
 
-		newUnObs := []chan<- Reply{}
-		for _, existing := range e.unObservers {
+		unObservers := e.unObservers
+		// in-place removing observer
+		newUnObs := unObservers[:0]
+		for i, existing := range unObservers {
+			unObservers[i] = nil // avoid memory leak of channel
 			if existing != o {
-				newUnObs = append(newUnObs, o)
+				newUnObs = append(newUnObs, existing)
 			}
 		}
 		e.unObservers = newUnObs
@@ -460,10 +463,12 @@ func (e *Engine) UnsubscribeAll(o chan Reply) {
 		}
 	}()
 	e.sendCommand(func() {
-		newUnObs := []chan<- Reply{}
-		for _, existing := range e.allObservers {
+		allObservers := e.allObservers
+		newUnObs := allObservers[:0]
+		for i, existing := range allObservers {
+			allObservers[i] = nil // avoid memory leak of channel
 			if existing != o {
-				newUnObs = append(newUnObs, o)
+				newUnObs = append(newUnObs, existing)
 			}
 		}
 		e.allObservers = newUnObs
diff --git a/engine_test.go b/engine_test.go
index 14e6ace..b796557 100644
--- a/engine_test.go
+++ b/engine_test.go
@@ -133,6 +133,31 @@ func TestConnect(t *testing.T) {
 	}
 }
 
+func TestUnsubscribeAllAndUnmatched(t *testing.T) {
+	engine := NewTestEngine(t)
+	defer engine.ConditionalStop(t)
+	dummy := make(chan Reply)
+	rc := make(chan Reply)
+	engine.SubscribeAll(dummy)
+	engine.SubscribeAll(rc)
+	engine.UnsubscribeAll(rc)
+	for _, v := range engine.allObservers {
+		if v == rc {
+			t.Log("rc should be unsubscribed from allObservers")
+			t.Fail()
+		}
+	}
+	engine.Subscribe(dummy, UnmatchedReplyID)
+	engine.Subscribe(rc, UnmatchedReplyID)
+	engine.Unsubscribe(rc, UnmatchedReplyID)
+	for _, v := range engine.unObservers {
+		if v == rc {
+			t.Log("rc should be unsubscribed from unObservers")
+			t.Fail()
+		}
+	}
+}
+
 func logreply(t *testing.T, reply Reply, err error) {
 	if reply == nil {
 		t.Logf("received reply nil")