diff --git a/iothub/device/src/IotHubConnectionString.Core.cs b/iothub/device/src/IotHubConnectionString.Core.cs
index 70edd63dd0..c9a59917e4 100644
--- a/iothub/device/src/IotHubConnectionString.Core.cs
+++ b/iothub/device/src/IotHubConnectionString.Core.cs
@@ -19,11 +19,11 @@ Task<string> IAuthorizationProvider.GetPasswordAsync()
                 if (Logging.IsEnabled)
                     Logging.Enter(this, $"{nameof(IotHubConnectionString)}.{nameof(IAuthorizationProvider.GetPasswordAsync)}");
 
-                Debug.Assert(TokenRefresher != null);
+                Debug.Assert(!string.IsNullOrWhiteSpace(SharedAccessSignature) || TokenRefresher != null, "Both can't be null");
 
                 return !string.IsNullOrWhiteSpace(SharedAccessSignature)
                     ? Task.FromResult(SharedAccessSignature)
-                    : TokenRefresher.GetTokenAsync(Audience);
+                    : TokenRefresher?.GetTokenAsync(Audience);
             }
             finally
             {