diff --git a/src/Hocon.API.Tests/HoconAPISpec.ApproveCore.approved.txt b/src/Hocon.API.Tests/HoconAPISpec.ApproveCore.approved.txt
index 9ca888e8..8dd27775 100644
--- a/src/Hocon.API.Tests/HoconAPISpec.ApproveCore.approved.txt
+++ b/src/Hocon.API.Tests/HoconAPISpec.ApproveCore.approved.txt
@@ -407,6 +407,7 @@ namespace Hocon
         public override Hocon.HoconType Type { get; }
         public System.Collections.Generic.IDictionary<string, object> Unwrapped { get; }
         public System.Collections.Generic.IEnumerable<Hocon.HoconElement> Values { get; }
+        [System.ObsoleteAttribute("Only used by Hyperion deserializer", true)]
         public void Add(string key, Hocon.HoconElement value) { }
         public void Add(System.Collections.Generic.KeyValuePair<string, Hocon.HoconElement> item) { }
         public virtual System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<string, Hocon.HoconElement>> AsEnumerable() { }
diff --git a/src/Hocon/HoconObject.cs b/src/Hocon/HoconObject.cs
index 6ef72265..b982fdc9 100644
--- a/src/Hocon/HoconObject.cs
+++ b/src/Hocon/HoconObject.cs
@@ -301,9 +301,10 @@ public override bool Equals(HoconElement other)
             return true;
         }
 
+        [Obsolete("Only used by Hyperion deserializer", true)]
         public void Add(string key, HoconElement value)
         {
-            throw new InvalidOperationException("HoconObject is a read only Dictionary.");
+            Fields = Fields.Add(key, value);
         }
 
         public bool Remove(string key)