diff --git a/collections-dictionary/UpdateDictionaryValue/Tests/Tests.csproj b/collections-dictionary/UpdateDictionaryValue/Tests/Tests.csproj
index 6b815efca5..da8cc3ab2b 100644
--- a/collections-dictionary/UpdateDictionaryValue/Tests/Tests.csproj
+++ b/collections-dictionary/UpdateDictionaryValue/Tests/Tests.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>net7.0</TargetFramework>
+    <TargetFramework>net10.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
 
@@ -9,10 +9,9 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.3.2" />
-    <PackageReference Include="MSTest.TestAdapter" Version="2.2.10" />
-    <PackageReference Include="MSTest.TestFramework" Version="2.2.10" />
-    <PackageReference Include="coverlet.collector" Version="3.1.2" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.10.1" />
+    <PackageReference Include="MSTest" Version="4.5.1" />
+    <PackageReference Include="coverlet.collector" Version="10.1.0" />
   </ItemGroup>
 
   <ItemGroup>
diff --git a/collections-dictionary/UpdateDictionaryValue/Tests/UpdateDictionaryValueUnitTests.cs b/collections-dictionary/UpdateDictionaryValue/Tests/UpdateDictionaryValueUnitTests.cs
index 069334fa67..b245b06592 100644
--- a/collections-dictionary/UpdateDictionaryValue/Tests/UpdateDictionaryValueUnitTests.cs
+++ b/collections-dictionary/UpdateDictionaryValue/Tests/UpdateDictionaryValueUnitTests.cs
@@ -1,3 +1,4 @@
+using System.Collections.Concurrent;
 using UpdateDictionaryValue;
 
 namespace Tests
@@ -35,5 +36,41 @@ public void GivenUpdatingNewToppingValue_ThenNewToppingIsAdded()
 
             Assert.AreEqual(12, dictionary.Toppings["mushroom"]);
         }
+
+        [TestMethod]
+        public void GivenExistingTopping_WhenAddToppingIfMissing_ThenValueIsUnchanged()
+        {
+            var dictionary = new ToppingsDictionary();
+
+            dictionary.AddToppingIfMissing("pepperoni", 100);
+            dictionary.AddToppingIfMissing("mushroom", 2);
+
+            Assert.AreEqual(4, dictionary.Toppings["pepperoni"]);
+            Assert.AreEqual(2, dictionary.Toppings["mushroom"]);
+        }
+
+        [TestMethod]
+        public void GivenNewAndExistingToppings_WhenAddToppingsByRef_ThenBothAreUpdated()
+        {
+            var dictionary = new ToppingsDictionary();
+
+            dictionary.AddToppingsByRef("mushroom", 5);
+            dictionary.AddToppingsByRef("pepperoni", 4);
+
+            Assert.AreEqual(5, dictionary.Toppings["mushroom"]);
+            Assert.AreEqual(8, dictionary.Toppings["pepperoni"]);
+        }
+
+        [TestMethod]
+        public void GivenConcurrentDictionary_WhenAddOrUpdate_ThenAddsThenUpdates()
+        {
+            var toppings = new ConcurrentDictionary<string, int>();
+
+            var first = toppings.AddOrUpdate("pepperoni", 4, (_, currentAmount) => currentAmount + 4);
+            var second = toppings.AddOrUpdate("pepperoni", 4, (_, currentAmount) => currentAmount + 4);
+
+            Assert.AreEqual(4, first);
+            Assert.AreEqual(8, second);
+        }
     }
 }
\ No newline at end of file
diff --git a/collections-dictionary/UpdateDictionaryValue/UpdateDictionaryValue/Program.cs b/collections-dictionary/UpdateDictionaryValue/UpdateDictionaryValue/Program.cs
index 7e8d7144f4..7b2342ea7f 100644
--- a/collections-dictionary/UpdateDictionaryValue/UpdateDictionaryValue/Program.cs
+++ b/collections-dictionary/UpdateDictionaryValue/UpdateDictionaryValue/Program.cs
@@ -1,20 +1,37 @@
-using UpdateDictionaryValue;
+using System.Collections.Concurrent;
+using UpdateDictionaryValue;
 
 var toppingsDictionary = new ToppingsDictionary();
 toppingsDictionary.AddToppings("pepperoni", 4);
+toppingsDictionary.AddToppings("olive", 3);
+
+PrintToppings(toppingsDictionary);
 
 try
 {
-    toppingsDictionary.Toppings["jalepeno"] = toppingsDictionary.Toppings["jalepeno"] + 1;
+    // The indexer-only version of AddToppings reads the value before it writes it
+    toppingsDictionary.Toppings["jalapeno"] = toppingsDictionary.Toppings["jalapeno"] + 1;
 }
-catch (Exception e)
+catch (KeyNotFoundException e)
 {
-    Console.WriteLine(e);
+    Console.WriteLine($"{e.GetType()}: {e.Message}");
 }
 
-toppingsDictionary.AddToppings("jalepeno", 1);
+toppingsDictionary.AddToppings("jalapeno", 1);
+
+PrintToppings(toppingsDictionary);
+
+var toppings = new ConcurrentDictionary<string, int>();
 
-foreach (var topping in toppingsDictionary.Toppings)
+Console.WriteLine(toppings.AddOrUpdate("pepperoni", 4, (_, currentAmount) => currentAmount + 4));
+Console.WriteLine(toppings.AddOrUpdate("pepperoni", 4, (_, currentAmount) => currentAmount + 4));
+
+static void PrintToppings(ToppingsDictionary toppingsDictionary)
 {
-    Console.WriteLine($"{topping.Key} = {topping.Value}");
-}
\ No newline at end of file
+    foreach (var topping in toppingsDictionary.Toppings)
+    {
+        Console.WriteLine($"{topping.Key} = {topping.Value}");
+    }
+
+    Console.WriteLine();
+}
diff --git a/collections-dictionary/UpdateDictionaryValue/UpdateDictionaryValue/ToppingsDictionary.cs b/collections-dictionary/UpdateDictionaryValue/UpdateDictionaryValue/ToppingsDictionary.cs
index 05ab025c0d..d7a8791371 100644
--- a/collections-dictionary/UpdateDictionaryValue/UpdateDictionaryValue/ToppingsDictionary.cs
+++ b/collections-dictionary/UpdateDictionaryValue/UpdateDictionaryValue/ToppingsDictionary.cs
@@ -1,8 +1,10 @@
-namespace UpdateDictionaryValue
+using System.Runtime.InteropServices;
+
+namespace UpdateDictionaryValue
 {
     public class ToppingsDictionary
     {
-        public Dictionary<string, int> Toppings { get; private set; }
+        public Dictionary<string, int> Toppings { get; }
 
         public ToppingsDictionary()
         {
@@ -25,5 +27,21 @@ public void AddToppings(string toppingType, int amount)
                 Toppings.Add(toppingType, amount);
             }
         }
+
+        public void AddToppingIfMissing(string toppingType, int amount)
+        {
+            if (!Toppings.TryAdd(toppingType, amount))
+            {
+                Console.WriteLine($"{toppingType} is already on the pizza.");
+            }
+        }
+
+        public void AddToppingsByRef(string toppingType, int amount)
+        {
+            ref var currentAmount = ref CollectionsMarshal
+                .GetValueRefOrAddDefault(Toppings, toppingType, out _);
+
+            currentAmount += amount;
+        }
     }
 }
diff --git a/collections-dictionary/UpdateDictionaryValue/UpdateDictionaryValue/UpdateDictionaryValue.csproj b/collections-dictionary/UpdateDictionaryValue/UpdateDictionaryValue/UpdateDictionaryValue.csproj
index f02677bf64..dfb40caafc 100644
--- a/collections-dictionary/UpdateDictionaryValue/UpdateDictionaryValue/UpdateDictionaryValue.csproj
+++ b/collections-dictionary/UpdateDictionaryValue/UpdateDictionaryValue/UpdateDictionaryValue.csproj
@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>net7.0</TargetFramework>
+    <TargetFramework>net10.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
   </PropertyGroup>