diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractCSharpCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractCSharpCodegen.java
index d39c6c07ab47..fb4a9c861b82 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractCSharpCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractCSharpCodegen.java
@@ -153,7 +153,7 @@ public abstract class AbstractCSharpCodegen extends DefaultCodegen implements Co
                         "DateTime?",
                         "DateTime",
                         "DateTimeOffset?",
-                        "DataTimeOffset",
+                        "DateTimeOffset",
                         "Boolean",
                         "Double",
                         "Int32",
@@ -192,7 +192,7 @@ public abstract class AbstractCSharpCodegen extends DefaultCodegen implements Co
 
         // nullable type
         nullableType = new HashSet<String>(
-                Arrays.asList("decimal", "bool", "int", "float", "long", "double", "DateTime", "Guid")
+                Arrays.asList("decimal", "bool", "int", "float", "long", "double", "DateTime", "DateTimeOffset", "Guid")
         );
         // value Types
         valueTypes = new HashSet<String>(
@@ -226,9 +226,9 @@ public abstract class AbstractCSharpCodegen extends DefaultCodegen implements Co
     public void useDateTimeOffset(boolean flag) {
         this.useDateTimeOffsetFlag = flag;
         if (flag) {
-            typeMapping.put("DateTime", "DateTimeOffset?");
+            typeMapping.put("DateTime", "DateTimeOffset");
         } else {
-            typeMapping.put("DateTime", "DateTime?");
+            typeMapping.put("DateTime", "DateTime");
         }
     }