diff --git a/src/NUnitFramework/framework/Constraints/DictionaryContainsKeyConstraint.cs b/src/NUnitFramework/framework/Constraints/DictionaryContainsKeyConstraint.cs
index c88bb34f58..2263def147 100644
--- a/src/NUnitFramework/framework/Constraints/DictionaryContainsKeyConstraint.cs
+++ b/src/NUnitFramework/framework/Constraints/DictionaryContainsKeyConstraint.cs
@@ -51,9 +51,9 @@ public DictionaryContainsKeyConstraint(object expected)
         /// Returns a new DictionaryContainsKeyValuePairConstraint checking for the
         /// presence of a particular key-value-pair in the dictionary.
         /// </summary>
-        public DictionaryContainsKeyValuePairConstraint WithValue(object expectedValue)
+        public DictionaryContainsKeyValuePairConstraint WithValue(object? expectedValue)
         {
-            return (DictionaryContainsKeyValuePairConstraint)Instead.Append(new DictionaryContainsKeyValuePairConstraint(Expected, expectedValue));
+            return Instead.Append(new DictionaryContainsKeyValuePairConstraint(Expected, expectedValue));
         }
 
         private bool Matches(object? actual)
diff --git a/src/NUnitFramework/framework/Constraints/DictionaryContainsKeyValuePairConstraint.cs b/src/NUnitFramework/framework/Constraints/DictionaryContainsKeyValuePairConstraint.cs
index 495cfe49c2..5022c90c54 100644
--- a/src/NUnitFramework/framework/Constraints/DictionaryContainsKeyValuePairConstraint.cs
+++ b/src/NUnitFramework/framework/Constraints/DictionaryContainsKeyValuePairConstraint.cs
@@ -19,7 +19,7 @@ public sealed class DictionaryContainsKeyValuePairConstraint : CollectionItemsEq
         /// <summary>
         /// Construct a DictionaryContainsKeyValuePairConstraint
         /// </summary>
-        public DictionaryContainsKeyValuePairConstraint(object key, object value)
+        public DictionaryContainsKeyValuePairConstraint(object key, object? value)
         {
             _expected = new DictionaryEntry(key, value);
         }