diff --git a/src/NJsonSchema.CodeGeneration.CSharp.Tests/AdditionalPropertiesTests.cs b/src/NJsonSchema.CodeGeneration.CSharp.Tests/AdditionalPropertiesTests.cs
index 0df010cfa..3066a0ddf 100644
--- a/src/NJsonSchema.CodeGeneration.CSharp.Tests/AdditionalPropertiesTests.cs
+++ b/src/NJsonSchema.CodeGeneration.CSharp.Tests/AdditionalPropertiesTests.cs
@@ -42,6 +42,7 @@ public async Task When_additionalProperties_schema_is_set_for_object_then_specia
             //// Assert
             Assert.Contains("[Newtonsoft.Json.JsonExtensionData]", code);
             Assert.Contains("public System.Collections.Generic.IDictionary<string, object> AdditionalProperties", code);
+            Assert.Contains("get { return _additionalProperties ?? (_additionalProperties = new System.Collections.Generic.Dictionary<string, object>()); }", code);
         }
 
         [Fact]
@@ -80,6 +81,7 @@ public async Task When_using_SystemTextJson_additionalProperties_schema_is_set_f
             //// Assert
             Assert.Contains("[System.Text.Json.Serialization.JsonExtensionData]", code);
             Assert.Contains("public System.Collections.Generic.IDictionary<string, object> AdditionalProperties", code);
+            Assert.Contains("get { return _additionalProperties ?? (_additionalProperties = new System.Collections.Generic.Dictionary<string, object>()); }", code);
         }
 
         [Fact]
diff --git a/src/NJsonSchema.CodeGeneration.CSharp/Templates/Class.liquid b/src/NJsonSchema.CodeGeneration.CSharp/Templates/Class.liquid
index ffd3baed5..41666803f 100644
--- a/src/NJsonSchema.CodeGeneration.CSharp/Templates/Class.liquid
+++ b/src/NJsonSchema.CodeGeneration.CSharp/Templates/Class.liquid
@@ -123,7 +123,7 @@
 
 {%- if GenerateAdditionalPropertiesProperty -%}
 
-    private System.Collections.Generic.IDictionary<string, {{ AdditionalPropertiesType }}> _additionalProperties = new System.Collections.Generic.Dictionary<string, {{ AdditionalPropertiesType }}>();
+    private System.Collections.Generic.IDictionary<string, {{ AdditionalPropertiesType }}>{% if GenerateNullableReferenceTypes %}?{% endif %} _additionalProperties;
 
 {%-       if UseSystemTextJson -%}
     [System.Text.Json.Serialization.JsonExtensionData]
@@ -132,7 +132,7 @@
 {%-       endif -%}
     public System.Collections.Generic.IDictionary<string, {{ AdditionalPropertiesType }}> AdditionalProperties
     {
-        get { return _additionalProperties; }
+        get { return _additionalProperties ?? (_additionalProperties = new System.Collections.Generic.Dictionary<string, {{ AdditionalPropertiesType }}>()); }
         {{PropertySetterAccessModifier}}set { _additionalProperties = value; }
     }