diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractKotlinCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractKotlinCodegen.java
index a00fc670c3c4..e980427505ef 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractKotlinCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractKotlinCodegen.java
@@ -416,6 +416,10 @@ public abstract class AbstractKotlinCodegen extends DefaultCodegen implements Co
             LOGGER.info("NOTE: To enable file post-processing, 'enablePostProcessFile' must be set to `true` (--enable-post-process-file for CLI).");
         }
 
+        if (additionalProperties.containsKey(MODEL_MUTABLE)) {
+            additionalProperties.put(MODEL_MUTABLE, Boolean.parseBoolean(additionalProperties.get(MODEL_MUTABLE).toString()));
+        }
+
         if (additionalProperties.containsKey(CodegenConstants.ENUM_PROPERTY_NAMING)) {
             setEnumPropertyNaming((String) additionalProperties.get(CodegenConstants.ENUM_PROPERTY_NAMING));
         }
diff --git a/samples/server/petstore/kotlin/vertx/src/main/kotlin/org/openapitools/server/api/model/Category.kt b/samples/server/petstore/kotlin/vertx/src/main/kotlin/org/openapitools/server/api/model/Category.kt
index 29aaa19c2c2f..7768072a83d8 100644
--- a/samples/server/petstore/kotlin/vertx/src/main/kotlin/org/openapitools/server/api/model/Category.kt
+++ b/samples/server/petstore/kotlin/vertx/src/main/kotlin/org/openapitools/server/api/model/Category.kt
@@ -24,8 +24,8 @@ import com.fasterxml.jackson.annotation.JsonInclude
 @JsonInclude(JsonInclude.Include.NON_NULL)
 @JsonIgnoreProperties(ignoreUnknown = true)
 data class Category (
-    var id: kotlin.Long? = null,
-    var name: kotlin.String? = null
+    val id: kotlin.Long? = null,
+    val name: kotlin.String? = null
 ) {
 
 }
diff --git a/samples/server/petstore/kotlin/vertx/src/main/kotlin/org/openapitools/server/api/model/ModelApiResponse.kt b/samples/server/petstore/kotlin/vertx/src/main/kotlin/org/openapitools/server/api/model/ModelApiResponse.kt
index ce8326960332..332a3c0f6e7b 100644
--- a/samples/server/petstore/kotlin/vertx/src/main/kotlin/org/openapitools/server/api/model/ModelApiResponse.kt
+++ b/samples/server/petstore/kotlin/vertx/src/main/kotlin/org/openapitools/server/api/model/ModelApiResponse.kt
@@ -25,9 +25,9 @@ import com.fasterxml.jackson.annotation.JsonInclude
 @JsonInclude(JsonInclude.Include.NON_NULL)
 @JsonIgnoreProperties(ignoreUnknown = true)
 data class ModelApiResponse (
-    var code: kotlin.Int? = null,
-    var type: kotlin.String? = null,
-    var message: kotlin.String? = null
+    val code: kotlin.Int? = null,
+    val type: kotlin.String? = null,
+    val message: kotlin.String? = null
 ) {
 
 }
diff --git a/samples/server/petstore/kotlin/vertx/src/main/kotlin/org/openapitools/server/api/model/Order.kt b/samples/server/petstore/kotlin/vertx/src/main/kotlin/org/openapitools/server/api/model/Order.kt
index a25f7e74bc7f..9078e0bdd256 100644
--- a/samples/server/petstore/kotlin/vertx/src/main/kotlin/org/openapitools/server/api/model/Order.kt
+++ b/samples/server/petstore/kotlin/vertx/src/main/kotlin/org/openapitools/server/api/model/Order.kt
@@ -28,13 +28,13 @@ import com.fasterxml.jackson.annotation.JsonInclude
 @JsonInclude(JsonInclude.Include.NON_NULL)
 @JsonIgnoreProperties(ignoreUnknown = true)
 data class Order (
-    var id: kotlin.Long? = null,
-    var petId: kotlin.Long? = null,
-    var quantity: kotlin.Int? = null,
-    var shipDate: java.time.OffsetDateTime? = null,
+    val id: kotlin.Long? = null,
+    val petId: kotlin.Long? = null,
+    val quantity: kotlin.Int? = null,
+    val shipDate: java.time.OffsetDateTime? = null,
     /* Order Status */
-    var status: Order.Status? = null,
-    var complete: kotlin.Boolean? = false
+    val status: Order.Status? = null,
+    val complete: kotlin.Boolean? = false
 ) {
 
     /**
diff --git a/samples/server/petstore/kotlin/vertx/src/main/kotlin/org/openapitools/server/api/model/Pet.kt b/samples/server/petstore/kotlin/vertx/src/main/kotlin/org/openapitools/server/api/model/Pet.kt
index e80d49fc3f5f..6061c8e01549 100644
--- a/samples/server/petstore/kotlin/vertx/src/main/kotlin/org/openapitools/server/api/model/Pet.kt
+++ b/samples/server/petstore/kotlin/vertx/src/main/kotlin/org/openapitools/server/api/model/Pet.kt
@@ -30,13 +30,13 @@ import com.fasterxml.jackson.annotation.JsonInclude
 @JsonInclude(JsonInclude.Include.NON_NULL)
 @JsonIgnoreProperties(ignoreUnknown = true)
 data class Pet (
-    @SerializedName("name") private var _name: kotlin.String?,
-    @SerializedName("photoUrls") private var _photoUrls: kotlin.Array<kotlin.String>?,
-    var id: kotlin.Long? = null,
-    var category: Category? = null,
-    var tags: kotlin.Array<Tag>? = null,
+    @SerializedName("name") private val _name: kotlin.String?,
+    @SerializedName("photoUrls") private val _photoUrls: kotlin.Array<kotlin.String>?,
+    val id: kotlin.Long? = null,
+    val category: Category? = null,
+    val tags: kotlin.Array<Tag>? = null,
     /* pet status in the store */
-    var status: Pet.Status? = null
+    val status: Pet.Status? = null
 ) {
 
     /**
@@ -53,9 +53,9 @@ data class Pet (
     
     }
 
-        var name get() = _name ?: throw IllegalArgumentException("name is required")
-                    set(value){ _name = value }
-        var photoUrls get() = _photoUrls ?: throw IllegalArgumentException("photoUrls is required")
-                    set(value){ _photoUrls = value }
+        val name get() = _name ?: throw IllegalArgumentException("name is required")
+                    
+        val photoUrls get() = _photoUrls ?: throw IllegalArgumentException("photoUrls is required")
+                    
 }
 
diff --git a/samples/server/petstore/kotlin/vertx/src/main/kotlin/org/openapitools/server/api/model/Tag.kt b/samples/server/petstore/kotlin/vertx/src/main/kotlin/org/openapitools/server/api/model/Tag.kt
index 359a53af6091..b444b341a9e3 100644
--- a/samples/server/petstore/kotlin/vertx/src/main/kotlin/org/openapitools/server/api/model/Tag.kt
+++ b/samples/server/petstore/kotlin/vertx/src/main/kotlin/org/openapitools/server/api/model/Tag.kt
@@ -24,8 +24,8 @@ import com.fasterxml.jackson.annotation.JsonInclude
 @JsonInclude(JsonInclude.Include.NON_NULL)
 @JsonIgnoreProperties(ignoreUnknown = true)
 data class Tag (
-    var id: kotlin.Long? = null,
-    var name: kotlin.String? = null
+    val id: kotlin.Long? = null,
+    val name: kotlin.String? = null
 ) {
 
 }
diff --git a/samples/server/petstore/kotlin/vertx/src/main/kotlin/org/openapitools/server/api/model/User.kt b/samples/server/petstore/kotlin/vertx/src/main/kotlin/org/openapitools/server/api/model/User.kt
index 791d0b882333..e8b5bb5e7051 100644
--- a/samples/server/petstore/kotlin/vertx/src/main/kotlin/org/openapitools/server/api/model/User.kt
+++ b/samples/server/petstore/kotlin/vertx/src/main/kotlin/org/openapitools/server/api/model/User.kt
@@ -30,15 +30,15 @@ import com.fasterxml.jackson.annotation.JsonInclude
 @JsonInclude(JsonInclude.Include.NON_NULL)
 @JsonIgnoreProperties(ignoreUnknown = true)
 data class User (
-    var id: kotlin.Long? = null,
-    var username: kotlin.String? = null,
-    var firstName: kotlin.String? = null,
-    var lastName: kotlin.String? = null,
-    var email: kotlin.String? = null,
-    var password: kotlin.String? = null,
-    var phone: kotlin.String? = null,
+    val id: kotlin.Long? = null,
+    val username: kotlin.String? = null,
+    val firstName: kotlin.String? = null,
+    val lastName: kotlin.String? = null,
+    val email: kotlin.String? = null,
+    val password: kotlin.String? = null,
+    val phone: kotlin.String? = null,
     /* User Status */
-    var userStatus: kotlin.Int? = null
+    val userStatus: kotlin.Int? = null
 ) {
 
 }