diff --git a/src/core/Akka.API.Tests/verify/CoreAPISpec.ApproveCore.DotNet.verified.txt b/src/core/Akka.API.Tests/verify/CoreAPISpec.ApproveCore.DotNet.verified.txt
index b16d008ad18..68130c8810e 100644
--- a/src/core/Akka.API.Tests/verify/CoreAPISpec.ApproveCore.DotNet.verified.txt
+++ b/src/core/Akka.API.Tests/verify/CoreAPISpec.ApproveCore.DotNet.verified.txt
@@ -5642,6 +5642,7 @@ namespace Akka.Util.Internal
     public class static Extensions
     {
         public static System.Collections.Generic.IDictionary<TKey, TValue> AddAndReturn<TKey, TValue>(this System.Collections.Generic.IDictionary<TKey, TValue> hash, TKey key, TValue value) { }
+        [System.ObsoleteAttribute("Use the dictionary setter directly")]
         public static void AddOrSet<TKey, TValue>(this System.Collections.Generic.IDictionary<TKey, TValue> hash, TKey key, TValue value) { }
         public static T AsInstanceOf<T>(this object self) { }
         public static string BetweenDoubleQuotes(this string self) { }
diff --git a/src/core/Akka.API.Tests/verify/CoreAPISpec.ApproveCore.Net.verified.txt b/src/core/Akka.API.Tests/verify/CoreAPISpec.ApproveCore.Net.verified.txt
index b1c6cb7b794..f109a52de5c 100644
--- a/src/core/Akka.API.Tests/verify/CoreAPISpec.ApproveCore.Net.verified.txt
+++ b/src/core/Akka.API.Tests/verify/CoreAPISpec.ApproveCore.Net.verified.txt
@@ -5631,6 +5631,7 @@ namespace Akka.Util.Internal
     public class static Extensions
     {
         public static System.Collections.Generic.IDictionary<TKey, TValue> AddAndReturn<TKey, TValue>(this System.Collections.Generic.IDictionary<TKey, TValue> hash, TKey key, TValue value) { }
+        [System.ObsoleteAttribute("Use the dictionary setter directly")]
         public static void AddOrSet<TKey, TValue>(this System.Collections.Generic.IDictionary<TKey, TValue> hash, TKey key, TValue value) { }
         public static T AsInstanceOf<T>(this object self) { }
         public static string BetweenDoubleQuotes(this string self) { }
diff --git a/src/core/Akka/Util/Internal/Extensions.cs b/src/core/Akka/Util/Internal/Extensions.cs
index 5e74be8e3c8..51924ee4e00 100644
--- a/src/core/Akka/Util/Internal/Extensions.cs
+++ b/src/core/Akka/Util/Internal/Extensions.cs
@@ -111,12 +111,10 @@ public static string BetweenDoubleQuotes(this string self)
         /// <param name="hash">TBD</param>
         /// <param name="key">TBD</param>
         /// <param name="value">TBD</param>
+        [Obsolete("Use the dictionary setter directly")]
         public static void AddOrSet<TKey, TValue>(this IDictionary<TKey, TValue> hash, TKey key, TValue value)
         {
-            if (hash.ContainsKey(key))
-                hash[key] = value;
-            else
-                hash.Add(key,value);
+            hash[key] = value;
         }
 
         /// <summary>
@@ -146,7 +144,7 @@ public static TValue GetOrElse<TKey, TValue>(this IDictionary<TKey, TValue> hash
         /// <returns>TBD</returns>
         public static IDictionary<TKey, TValue> AddAndReturn<TKey, TValue>(this IDictionary<TKey, TValue> hash, TKey key, TValue value)
         {
-            hash.AddOrSet(key, value);
+            hash[key] = value;
             return hash;
         }