diff --git a/dotnet/src/webdriver/Command.cs b/dotnet/src/webdriver/Command.cs
index 409c393860d6c..e6d7c422cbc1e 100644
--- a/dotnet/src/webdriver/Command.cs
+++ b/dotnet/src/webdriver/Command.cs
@@ -159,6 +159,7 @@ private static Dictionary<string, object> ConvertParametersFromJson(string value
     [JsonSerializable(typeof(byte[]))]
     [JsonSerializable(typeof(Dictionary<string, object>))]
     [JsonSerializable(typeof(Cookie))]
+    [JsonSerializable(typeof(ReturnedCookie))]
     [JsonSerializable(typeof(Proxy))]
     internal partial class CommandJsonSerializerContext : JsonSerializerContext
     {