diff --git a/internal/backends/memory/user.go b/internal/backends/memory/user.go
index eb2fd25..b08d535 100644
--- a/internal/backends/memory/user.go
+++ b/internal/backends/memory/user.go
@@ -190,8 +190,8 @@ func (user *User) LeaveRoom(room internal.Room) models.ApiError {
 func (user *User) SendMessage(room internal.Room, text string) models.ApiError {
 	memRoom := room.(*Room)
 
-	memRoom.mutex.Lock()
-	defer memRoom.mutex.Unlock()
+	memRoom.mutex.RLock()
+	defer memRoom.mutex.RUnlock()
 
 	userInRoom := false
 	for _, roomMember := range memRoom.joined {