diff --git a/CryptoExchange.Net/TimeOffsetManager.cs b/CryptoExchange.Net/TimeOffsetManager.cs
index 12f2746..66b9a00 100644
--- a/CryptoExchange.Net/TimeOffsetManager.cs
+++ b/CryptoExchange.Net/TimeOffsetManager.cs
@@ -113,7 +113,8 @@ namespace CryptoExchange.Net
         /// <param name="api"></param>
         internal static void RegisterRestApi(string api)
         {
-            _lastRestDelays[api] = new RestTimeOffset();
+            if (!_lastRestDelays.ContainsKey(api))
+                _lastRestDelays.TryAdd(api, new RestTimeOffset());
         }
 
         /// <summary>