diff --git a/src/Microsoft.Extensions.Configuration.AzureAppConfiguration/AzureAppConfigurationRefreshOptions.cs b/src/Microsoft.Extensions.Configuration.AzureAppConfiguration/AzureAppConfigurationRefreshOptions.cs
index 95b162e2..5297507c 100644
--- a/src/Microsoft.Extensions.Configuration.AzureAppConfiguration/AzureAppConfigurationRefreshOptions.cs
+++ b/src/Microsoft.Extensions.Configuration.AzureAppConfiguration/AzureAppConfigurationRefreshOptions.cs
@@ -35,6 +35,11 @@ public AzureAppConfigurationRefreshOptions Register(string key, bool refreshAll)
         /// <param name="refreshAll">If true, a change in the value of this key refreshes all key-values being used by the configuration provider.</param>
         public AzureAppConfigurationRefreshOptions Register(string key, string label = LabelFilter.Null, bool refreshAll = false)
         {
+            if (string.IsNullOrEmpty(key))
+            {
+                throw new ArgumentNullException(nameof(key));
+            }
+
             RefreshRegistrations.Add(new KeyValueWatcher
             {
                 Key = key,