diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/CSharpClientCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/CSharpClientCodegen.java
index bc5f04282c7..f3f37de36d4 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/CSharpClientCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/CSharpClientCodegen.java
@@ -369,7 +369,7 @@ public class CSharpClientCodegen extends AbstractCSharpCodegen {
     protected Set<String> getNullableTypes() {
         return GENERICHOST.equals(getLibrary())
                 ? super.getNullableTypes()
-                : new HashSet<>(Arrays.asList("decimal", "bool", "int", "uint", "long", "ulong", "float", "double", "DateTime", "DateTimeOffset", "Guid"));
+                : new HashSet<>(Arrays.asList("decimal", "bool", "int", "uint", "long", "ulong", "float", "double", "DateTime", "DateOnly", "DateTimeOffset", "Guid"));
     }
 
     @Override