diff --git a/Src/Newtonsoft.Json.Tests/Issues/Issue2450.cs b/Src/Newtonsoft.Json.Tests/Issues/Issue2450.cs
new file mode 100644
index 00000000..ee744c90
--- /dev/null
+++ b/Src/Newtonsoft.Json.Tests/Issues/Issue2450.cs
@@ -0,0 +1,97 @@
+#region License
+// Copyright (c) 2007 James Newton-King
+//
+// Permission is hereby granted, free of charge, to any person
+// obtaining a copy of this software and associated documentation
+// files (the "Software"), to deal in the Software without
+// restriction, including without limitation the rights to use,
+// copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the
+// Software is furnished to do so, subject to the following
+// conditions:
+//
+// The above copyright notice and this permission notice shall be
+// included in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+// OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+// HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+// WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+// OTHER DEALINGS IN THE SOFTWARE.
+#endregion
+
+#if (NET45 || NET50)
+#if DNXCORE50
+using Xunit;
+using Test = Xunit.FactAttribute;
+using Assert = Newtonsoft.Json.Tests.XUnitAssert;
+#else
+using NUnit.Framework;
+#endif
+using System.Collections.Generic;
+using Newtonsoft.Json.Serialization;
+using Newtonsoft.Json.Converters;
+using System.Collections;
+using System;
+
+namespace Newtonsoft.Json.Tests.Issues
+{
+    [TestFixture]
+    public class Issue2450
+    {
+        [Test]
+        public void Test()
+        {
+            var resolver = new DefaultContractResolver();
+            JsonContract contract;
+
+            contract = resolver.ResolveContract(typeof(Dict));
+            Assert.IsTrue(contract is JsonDictionaryContract);
+
+            contract = resolver.ResolveContract(typeof(Dict?));
+            Assert.IsTrue(contract is JsonDictionaryContract);
+        }
+
+        [Test]
+        public void Test_Serialize()
+        {
+            Dict d = new Dict(new Dictionary<string, object>
+            {
+                ["prop1"] = 1,
+                ["prop2"] = 2
+            });
+
+            string json = JsonConvert.SerializeObject(d);
+            Assert.AreEqual(@"{""prop1"":1,""prop2"":2}", json);
+        }
+
+        [Test]
+        public void Test_Deserialize()
+        {
+            string json = @"{""prop1"":1,""prop2"":2}";
+
+            var d = JsonConvert.DeserializeObject<Dict?>(json);
+            Assert.AreEqual(1, d.Value["prop1"]);
+            Assert.AreEqual(2, d.Value["prop2"]);
+        }
+
+        public struct Dict : IReadOnlyDictionary<string, object>
+        {
+            private readonly IDictionary<string, object> _dict;
+            public Dict(IDictionary<string, object> dict) => _dict = dict;
+
+            public object this[string key] => _dict[key];
+            public IEnumerable<string> Keys => _dict.Keys;
+            public IEnumerable<object> Values => _dict.Values;
+            public int Count => _dict.Count;
+            public bool ContainsKey(string key) => _dict.ContainsKey(key);
+            public IEnumerator<KeyValuePair<string, object>> GetEnumerator() => _dict.GetEnumerator();
+            public bool TryGetValue(string key, out object value) => _dict.TryGetValue(key, out value);
+            IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
+        }
+    }
+}
+#endif
\ No newline at end of file
diff --git a/Src/Newtonsoft.Json/Serialization/JsonDictionaryContract.cs b/Src/Newtonsoft.Json/Serialization/JsonDictionaryContract.cs
index cd92eacf..6c5afbe1 100644
--- a/Src/Newtonsoft.Json/Serialization/JsonDictionaryContract.cs
+++ b/Src/Newtonsoft.Json/Serialization/JsonDictionaryContract.cs
@@ -118,21 +118,21 @@ namespace Newtonsoft.Json.Serialization
             Type? keyType;
             Type? valueType;
 
-            if (ReflectionUtils.ImplementsGenericDefinition(underlyingType, typeof(IDictionary<,>), out _genericCollectionDefinitionType))
+            if (ReflectionUtils.ImplementsGenericDefinition(NonNullableUnderlyingType, typeof(IDictionary<,>), out _genericCollectionDefinitionType))
             {
                 keyType = _genericCollectionDefinitionType.GetGenericArguments()[0];
                 valueType = _genericCollectionDefinitionType.GetGenericArguments()[1];
 
-                if (ReflectionUtils.IsGenericDefinition(UnderlyingType, typeof(IDictionary<,>)))
+                if (ReflectionUtils.IsGenericDefinition(NonNullableUnderlyingType, typeof(IDictionary<,>)))
                 {
                     CreatedType = typeof(Dictionary<,>).MakeGenericType(keyType, valueType);
                 }
-                else if (underlyingType.IsGenericType())
+                else if (NonNullableUnderlyingType.IsGenericType())
                 {
                     // ConcurrentDictionary<,> + IDictionary setter + null value = error
                     // wrap to use generic setter
                     // https://github.com/JamesNK/Newtonsoft.Json/issues/1582
-                    Type typeDefinition = underlyingType.GetGenericTypeDefinition();
+                    Type typeDefinition = NonNullableUnderlyingType.GetGenericTypeDefinition();
                     if (typeDefinition.FullName == JsonTypeReflector.ConcurrentDictionaryTypeName)
                     {
                         ShouldCreateWrapper = true;
@@ -140,17 +140,17 @@ namespace Newtonsoft.Json.Serialization
                 }
 
 #if HAVE_READ_ONLY_COLLECTIONS
-                IsReadOnlyOrFixedSize = ReflectionUtils.InheritsGenericDefinition(underlyingType, typeof(ReadOnlyDictionary<,>));
+                IsReadOnlyOrFixedSize = ReflectionUtils.InheritsGenericDefinition(NonNullableUnderlyingType, typeof(ReadOnlyDictionary<,>));
 #endif
 
             }
 #if HAVE_READ_ONLY_COLLECTIONS
-            else if (ReflectionUtils.ImplementsGenericDefinition(underlyingType, typeof(IReadOnlyDictionary<,>), out _genericCollectionDefinitionType))
+            else if (ReflectionUtils.ImplementsGenericDefinition(NonNullableUnderlyingType, typeof(IReadOnlyDictionary<,>), out _genericCollectionDefinitionType))
             {
                 keyType = _genericCollectionDefinitionType.GetGenericArguments()[0];
                 valueType = _genericCollectionDefinitionType.GetGenericArguments()[1];
 
-                if (ReflectionUtils.IsGenericDefinition(UnderlyingType, typeof(IReadOnlyDictionary<,>)))
+                if (ReflectionUtils.IsGenericDefinition(NonNullableUnderlyingType, typeof(IReadOnlyDictionary<,>)))
                 {
                     CreatedType = typeof(ReadOnlyDictionary<,>).MakeGenericType(keyType, valueType);
                 }
@@ -160,9 +160,9 @@ namespace Newtonsoft.Json.Serialization
 #endif
             else
             {
-                ReflectionUtils.GetDictionaryKeyValueTypes(UnderlyingType, out keyType, out valueType);
+                ReflectionUtils.GetDictionaryKeyValueTypes(NonNullableUnderlyingType, out keyType, out valueType);
 
-                if (UnderlyingType == typeof(IDictionary))
+                if (NonNullableUnderlyingType == typeof(IDictionary))
                 {
                     CreatedType = typeof(Dictionary<object, object>);
                 }
@@ -176,9 +176,9 @@ namespace Newtonsoft.Json.Serialization
                     typeof(IDictionary<,>).MakeGenericType(keyType, valueType));
 
 #if HAVE_FSHARP_TYPES
-                if (!HasParameterizedCreatorInternal && underlyingType.Name == FSharpUtils.FSharpMapTypeName)
+                if (!HasParameterizedCreatorInternal && NonNullableUnderlyingType.Name == FSharpUtils.FSharpMapTypeName)
                 {
-                    FSharpUtils.EnsureInitialized(underlyingType.Assembly());
+                    FSharpUtils.EnsureInitialized(NonNullableUnderlyingType.Assembly());
                     _parameterizedCreator = FSharpUtils.Instance.CreateMap(keyType, valueType);
                 }
 #endif
@@ -207,7 +207,7 @@ namespace Newtonsoft.Json.Serialization
             if (DictionaryKeyType != null && 
                 DictionaryValueType != null &&
                 ImmutableCollectionsUtils.TryBuildImmutableForDictionaryContract(
-                    underlyingType,
+                    NonNullableUnderlyingType,
                     DictionaryKeyType,
                     DictionaryValueType,
                     out Type? immutableCreatedType,