diff --git a/modules/openapi-generator/src/main/resources/kotlin-client/anyof_class.mustache b/modules/openapi-generator/src/main/resources/kotlin-client/anyof_class.mustache
index 9804f8c261c9..56786362a309 100644
--- a/modules/openapi-generator/src/main/resources/kotlin-client/anyof_class.mustache
+++ b/modules/openapi-generator/src/main/resources/kotlin-client/anyof_class.mustache
@@ -185,7 +185,7 @@ import java.io.IOException
                         for(element in jsonElement.getAsJsonArray()) {
                         {{#items}}
                         {{#isNumber}}
-                            require(jsonElement.getAsJsonPrimitive().isNumber) {
+                            require(element.getAsJsonPrimitive().isNumber) {
                                 String.format("Expected json element to be of type Number in the JSON string but got `%s`", jsonElement.toString())
                             }
                         {{/isNumber}}
@@ -238,4 +238,96 @@ import java.io.IOException
             }.nullSafe() as TypeAdapter<T>
         }
     }
+
+    companion object {
+        /**
+        * Validates the JSON Element and throws an exception if issues found
+        *
+        * @param jsonElement JSON Element
+        * @throws IOException if the JSON Element is invalid with respect to {{classname}}
+        */
+        @Throws(IOException::class)
+        fun validateJsonElement(jsonElement: JsonElement?) {
+            var match = 0
+            val errorMessages = ArrayList<String>()
+            {{#composedSchemas}}
+            {{#anyOf}}
+            {{^vendorExtensions.x-duplicated-data-type}}
+            {{^hasVars}}
+            // validate the json string with {{{dataType}}}
+            try {
+                // validate the JSON object to see if any exception is thrown
+            {{^isArray}}
+            {{#isNumber}}
+                require(jsonElement!!.getAsJsonPrimitive().isNumber()) {
+                    String.format("Expected json element to be of type Number in the JSON string but got `%s`", jsonElement.toString())
+                }
+            {{/isNumber}}
+            {{^isNumber}}
+            {{#isPrimitiveType}}
+                require(jsonElement!!.getAsJsonPrimitive().is{{#isBoolean}}Boolean{{/isBoolean}}{{#isString}}String{{/isString}}{{^isString}}{{^isBoolean}}Number{{/isBoolean}}{{/isString}}()) {
+                    String.format("Expected json element to be of type {{#isBoolean}}Boolean{{/isBoolean}}{{#isString}}String{{/isString}}{{^isString}}{{^isBoolean}}Number{{/isBoolean}}{{/isString}} in the JSON string but got `%s`", jsonElement.toString())
+                }
+            {{/isPrimitiveType}}
+            {{/isNumber}}
+            {{^isNumber}}
+            {{^isPrimitiveType}}
+                {{{dataType}}}.validateJsonElement(jsonElement)
+            {{/isPrimitiveType}}
+            {{/isNumber}}
+            {{/isArray}}
+            {{#isArray}}
+                require(jsonElement!!.isJsonArray) {
+                    String.format("Expected json element to be a array type in the JSON string but got `%s`", jsonElement.toString())
+                }
+
+                // validate array items
+                for(element in jsonElement.getAsJsonArray()) {
+                {{#items}}
+                {{#isNumber}}
+                    require(element.getAsJsonPrimitive().isNumber) {
+                        String.format("Expected json element to be of type Number in the JSON string but got `%s`", jsonElement.toString())
+                    }
+                {{/isNumber}}
+                {{^isNumber}}
+                {{#isPrimitiveType}}
+                    require(element.getAsJsonPrimitive().is{{#isBoolean}}Boolean{{/isBoolean}}{{#isString}}String{{/isString}}{{^isString}}{{^isBoolean}}Number{{/isBoolean}}{{/isString}}) {
+                        String.format("Expected array items to be of type {{#isBoolean}}Boolean{{/isBoolean}}{{#isString}}String{{/isString}}{{^isString}}{{^isBoolean}}Number{{/isBoolean}}{{/isString}} in the JSON string but got `%s`", jsonElement.toString())
+                    }
+                {{/isPrimitiveType}}
+                {{/isNumber}}
+                {{^isNumber}}
+                {{^isPrimitiveType}}
+                    {{{dataType}}}.validateJsonElement(element)
+                {{/isPrimitiveType}}
+                {{/isNumber}}
+                {{/items}}
+                }
+            {{/isArray}}
+                match++
+            } catch (e: Exception) {
+                // Validation failed, continue
+                errorMessages.add(String.format("Validation for {{{dataType}}} failed with `%s`.", e.message))
+            }
+            {{/hasVars}}
+            {{#hasVars}}
+            // validate json string for {{{.}}}
+            try {
+                // validate the JSON object to see if any exception is thrown
+                {{.}}.validateJsonElement(jsonElement)
+                match++
+            } catch (e: Exception) {
+                // validation failed, continue
+                errorMessages.add(String.format("Validation for {{{.}}} failed with `%s`.", e.message))
+            }
+            {{/hasVars}}
+            {{/vendorExtensions.x-duplicated-data-type}}
+            {{/anyOf}}
+            {{/composedSchemas}}
+
+            if (match != 1) {
+                throw IOException(String.format("Failed validation for {{classname}}: %d classes match result, expected 1. Detailed failure message for oneOf schemas: %s. JSON: %s", match, errorMessages, jsonElement.toString()))
+            }
+        }
+    }
 }
\ No newline at end of file
diff --git a/modules/openapi-generator/src/main/resources/kotlin-client/oneof_class.mustache b/modules/openapi-generator/src/main/resources/kotlin-client/oneof_class.mustache
index ae6cff2298b7..a1e71c548272 100644
--- a/modules/openapi-generator/src/main/resources/kotlin-client/oneof_class.mustache
+++ b/modules/openapi-generator/src/main/resources/kotlin-client/oneof_class.mustache
@@ -179,7 +179,7 @@ import java.io.IOException
                         for(element in jsonElement.getAsJsonArray()) {
                         {{#items}}
                         {{#isNumber}}
-                            require(jsonElement.getAsJsonPrimitive().isNumber) {
+                            require(element.getAsJsonPrimitive().isNumber) {
                                 String.format("Expected json element to be of type Number in the JSON string but got `%s`", jsonElement.toString())
                             }
                         {{/isNumber}}
@@ -236,4 +236,96 @@ import java.io.IOException
             }.nullSafe() as TypeAdapter<T>
         }
     }
+
+    companion object {
+        /**
+        * Validates the JSON Element and throws an exception if issues found
+        *
+        * @param jsonElement JSON Element
+        * @throws IOException if the JSON Element is invalid with respect to {{classname}}
+        */
+        @Throws(IOException::class)
+        fun validateJsonElement(jsonElement: JsonElement?) {
+            var match = 0
+            val errorMessages = ArrayList<String>()
+            {{#composedSchemas}}
+            {{#oneOf}}
+            {{^vendorExtensions.x-duplicated-data-type}}
+            {{^hasVars}}
+            // validate the json string with {{{dataType}}}
+            try {
+                // validate the JSON object to see if any exception is thrown
+            {{^isArray}}
+            {{#isNumber}}
+                require(jsonElement!!.getAsJsonPrimitive().isNumber()) {
+                    String.format("Expected json element to be of type Number in the JSON string but got `%s`", jsonElement.toString())
+                }
+            {{/isNumber}}
+            {{^isNumber}}
+            {{#isPrimitiveType}}
+                require(jsonElement!!.getAsJsonPrimitive().is{{#isBoolean}}Boolean{{/isBoolean}}{{#isString}}String{{/isString}}{{^isString}}{{^isBoolean}}Number{{/isBoolean}}{{/isString}}()) {
+                    String.format("Expected json element to be of type {{#isBoolean}}Boolean{{/isBoolean}}{{#isString}}String{{/isString}}{{^isString}}{{^isBoolean}}Number{{/isBoolean}}{{/isString}} in the JSON string but got `%s`", jsonElement.toString())
+                }
+            {{/isPrimitiveType}}
+            {{/isNumber}}
+            {{^isNumber}}
+            {{^isPrimitiveType}}
+                {{{dataType}}}.validateJsonElement(jsonElement)
+            {{/isPrimitiveType}}
+            {{/isNumber}}
+            {{/isArray}}
+            {{#isArray}}
+                require(jsonElement!!.isJsonArray) {
+                    String.format("Expected json element to be a array type in the JSON string but got `%s`", jsonElement.toString())
+                }
+
+                // validate array items
+                for(element in jsonElement!!.getAsJsonArray()) {
+                {{#items}}
+                {{#isNumber}}
+                    require(jsonElement!!.getAsJsonPrimitive().isNumber) {
+                        String.format("Expected json element to be of type Number in the JSON string but got `%s`", jsonElement.toString())
+                    }
+                {{/isNumber}}
+                {{^isNumber}}
+                {{#isPrimitiveType}}
+                    require(element.getAsJsonPrimitive().is{{#isBoolean}}Boolean{{/isBoolean}}{{#isString}}String{{/isString}}{{^isString}}{{^isBoolean}}Number{{/isBoolean}}{{/isString}}) {
+                        String.format("Expected array items to be of type {{#isBoolean}}Boolean{{/isBoolean}}{{#isString}}String{{/isString}}{{^isString}}{{^isBoolean}}Number{{/isBoolean}}{{/isString}} in the JSON string but got `%s`", jsonElement.toString())
+                    }
+                {{/isPrimitiveType}}
+                {{/isNumber}}
+                {{^isNumber}}
+                {{^isPrimitiveType}}
+                    {{{dataType}}}.validateJsonElement(element)
+                {{/isPrimitiveType}}
+                {{/isNumber}}
+                {{/items}}
+                }
+            {{/isArray}}
+                match++
+            } catch (e: Exception) {
+                // Validation failed, continue
+                errorMessages.add(String.format("Validation for {{{dataType}}} failed with `%s`.", e.message))
+            }
+            {{/hasVars}}
+            {{#hasVars}}
+            // validate json string for {{{.}}}
+            try {
+                // validate the JSON object to see if any exception is thrown
+                {{.}}.validateJsonElement(jsonElement)
+                match++
+            } catch (e: Exception) {
+                // validation failed, continue
+                errorMessages.add(String.format("Validation for {{{.}}} failed with `%s`.", e.message))
+            }
+            {{/hasVars}}
+            {{/vendorExtensions.x-duplicated-data-type}}
+            {{/oneOf}}
+            {{/composedSchemas}}
+
+            if (match != 1) {
+                throw IOException(String.format("Failed validation for {{classname}}: %d classes match result, expected 1. Detailed failure message for oneOf schemas: %s. JSON: %s", match, errorMessages, jsonElement.toString()))
+            }
+        }
+    }
 }
\ No newline at end of file
diff --git a/samples/client/petstore/kotlin-model-prefix-type-mappings/src/main/kotlin/org/openapitools/client/models/ApiAnyOfUserOrPet.kt b/samples/client/petstore/kotlin-model-prefix-type-mappings/src/main/kotlin/org/openapitools/client/models/ApiAnyOfUserOrPet.kt
index 3d523a450eac..2e93ea377168 100644
--- a/samples/client/petstore/kotlin-model-prefix-type-mappings/src/main/kotlin/org/openapitools/client/models/ApiAnyOfUserOrPet.kt
+++ b/samples/client/petstore/kotlin-model-prefix-type-mappings/src/main/kotlin/org/openapitools/client/models/ApiAnyOfUserOrPet.kt
@@ -111,4 +111,40 @@ data class ApiAnyOfUserOrPet(var actualInstance: Any? = null) {
             }.nullSafe() as TypeAdapter<T>
         }
     }
+
+    companion object {
+        /**
+        * Validates the JSON Element and throws an exception if issues found
+        *
+        * @param jsonElement JSON Element
+        * @throws IOException if the JSON Element is invalid with respect to ApiAnyOfUserOrPet
+        */
+        @Throws(IOException::class)
+        fun validateJsonElement(jsonElement: JsonElement?) {
+            var match = 0
+            val errorMessages = ArrayList<String>()
+            // validate the json string with ApiUser
+            try {
+                // validate the JSON object to see if any exception is thrown
+                ApiUser.validateJsonElement(jsonElement)
+                match++
+            } catch (e: Exception) {
+                // Validation failed, continue
+                errorMessages.add(String.format("Validation for ApiUser failed with `%s`.", e.message))
+            }
+            // validate the json string with ApiPet
+            try {
+                // validate the JSON object to see if any exception is thrown
+                ApiPet.validateJsonElement(jsonElement)
+                match++
+            } catch (e: Exception) {
+                // Validation failed, continue
+                errorMessages.add(String.format("Validation for ApiPet failed with `%s`.", e.message))
+            }
+
+            if (match != 1) {
+                throw IOException(String.format("Failed validation for ApiAnyOfUserOrPet: %d classes match result, expected 1. Detailed failure message for oneOf schemas: %s. JSON: %s", match, errorMessages, jsonElement.toString()))
+            }
+        }
+    }
 }
diff --git a/samples/client/petstore/kotlin-model-prefix-type-mappings/src/main/kotlin/org/openapitools/client/models/ApiAnyOfUserOrPetOrArrayString.kt b/samples/client/petstore/kotlin-model-prefix-type-mappings/src/main/kotlin/org/openapitools/client/models/ApiAnyOfUserOrPetOrArrayString.kt
index 1ec7549f45c0..976630c764e1 100644
--- a/samples/client/petstore/kotlin-model-prefix-type-mappings/src/main/kotlin/org/openapitools/client/models/ApiAnyOfUserOrPetOrArrayString.kt
+++ b/samples/client/petstore/kotlin-model-prefix-type-mappings/src/main/kotlin/org/openapitools/client/models/ApiAnyOfUserOrPetOrArrayString.kt
@@ -144,4 +144,58 @@ data class ApiAnyOfUserOrPetOrArrayString(var actualInstance: Any? = null) {
             }.nullSafe() as TypeAdapter<T>
         }
     }
+
+    companion object {
+        /**
+        * Validates the JSON Element and throws an exception if issues found
+        *
+        * @param jsonElement JSON Element
+        * @throws IOException if the JSON Element is invalid with respect to ApiAnyOfUserOrPetOrArrayString
+        */
+        @Throws(IOException::class)
+        fun validateJsonElement(jsonElement: JsonElement?) {
+            var match = 0
+            val errorMessages = ArrayList<String>()
+            // validate the json string with ApiUser
+            try {
+                // validate the JSON object to see if any exception is thrown
+                ApiUser.validateJsonElement(jsonElement)
+                match++
+            } catch (e: Exception) {
+                // Validation failed, continue
+                errorMessages.add(String.format("Validation for ApiUser failed with `%s`.", e.message))
+            }
+            // validate the json string with ApiPet
+            try {
+                // validate the JSON object to see if any exception is thrown
+                ApiPet.validateJsonElement(jsonElement)
+                match++
+            } catch (e: Exception) {
+                // Validation failed, continue
+                errorMessages.add(String.format("Validation for ApiPet failed with `%s`.", e.message))
+            }
+            // validate the json string with kotlin.collections.List<kotlin.String>
+            try {
+                // validate the JSON object to see if any exception is thrown
+                require(jsonElement!!.isJsonArray) {
+                    String.format("Expected json element to be a array type in the JSON string but got `%s`", jsonElement.toString())
+                }
+
+                // validate array items
+                for(element in jsonElement.getAsJsonArray()) {
+                    require(element.getAsJsonPrimitive().isString) {
+                        String.format("Expected array items to be of type String in the JSON string but got `%s`", jsonElement.toString())
+                    }
+                }
+                match++
+            } catch (e: Exception) {
+                // Validation failed, continue
+                errorMessages.add(String.format("Validation for kotlin.collections.List<kotlin.String> failed with `%s`.", e.message))
+            }
+
+            if (match != 1) {
+                throw IOException(String.format("Failed validation for ApiAnyOfUserOrPetOrArrayString: %d classes match result, expected 1. Detailed failure message for oneOf schemas: %s. JSON: %s", match, errorMessages, jsonElement.toString()))
+            }
+        }
+    }
 }
diff --git a/samples/client/petstore/kotlin-model-prefix-type-mappings/src/main/kotlin/org/openapitools/client/models/ApiUserOrPet.kt b/samples/client/petstore/kotlin-model-prefix-type-mappings/src/main/kotlin/org/openapitools/client/models/ApiUserOrPet.kt
index 372906b0e56b..20db8006347b 100644
--- a/samples/client/petstore/kotlin-model-prefix-type-mappings/src/main/kotlin/org/openapitools/client/models/ApiUserOrPet.kt
+++ b/samples/client/petstore/kotlin-model-prefix-type-mappings/src/main/kotlin/org/openapitools/client/models/ApiUserOrPet.kt
@@ -115,4 +115,40 @@ data class ApiUserOrPet(var actualInstance: Any? = null) {
             }.nullSafe() as TypeAdapter<T>
         }
     }
+
+    companion object {
+        /**
+        * Validates the JSON Element and throws an exception if issues found
+        *
+        * @param jsonElement JSON Element
+        * @throws IOException if the JSON Element is invalid with respect to ApiUserOrPet
+        */
+        @Throws(IOException::class)
+        fun validateJsonElement(jsonElement: JsonElement?) {
+            var match = 0
+            val errorMessages = ArrayList<String>()
+            // validate the json string with ApiUser
+            try {
+                // validate the JSON object to see if any exception is thrown
+                ApiUser.validateJsonElement(jsonElement)
+                match++
+            } catch (e: Exception) {
+                // Validation failed, continue
+                errorMessages.add(String.format("Validation for ApiUser failed with `%s`.", e.message))
+            }
+            // validate the json string with ApiPet
+            try {
+                // validate the JSON object to see if any exception is thrown
+                ApiPet.validateJsonElement(jsonElement)
+                match++
+            } catch (e: Exception) {
+                // Validation failed, continue
+                errorMessages.add(String.format("Validation for ApiPet failed with `%s`.", e.message))
+            }
+
+            if (match != 1) {
+                throw IOException(String.format("Failed validation for ApiUserOrPet: %d classes match result, expected 1. Detailed failure message for oneOf schemas: %s. JSON: %s", match, errorMessages, jsonElement.toString()))
+            }
+        }
+    }
 }
diff --git a/samples/client/petstore/kotlin-model-prefix-type-mappings/src/main/kotlin/org/openapitools/client/models/ApiUserOrPetOrArrayString.kt b/samples/client/petstore/kotlin-model-prefix-type-mappings/src/main/kotlin/org/openapitools/client/models/ApiUserOrPetOrArrayString.kt
index 009b3bef5230..9a5b06b2a9a5 100644
--- a/samples/client/petstore/kotlin-model-prefix-type-mappings/src/main/kotlin/org/openapitools/client/models/ApiUserOrPetOrArrayString.kt
+++ b/samples/client/petstore/kotlin-model-prefix-type-mappings/src/main/kotlin/org/openapitools/client/models/ApiUserOrPetOrArrayString.kt
@@ -147,4 +147,58 @@ data class ApiUserOrPetOrArrayString(var actualInstance: Any? = null) {
             }.nullSafe() as TypeAdapter<T>
         }
     }
+
+    companion object {
+        /**
+        * Validates the JSON Element and throws an exception if issues found
+        *
+        * @param jsonElement JSON Element
+        * @throws IOException if the JSON Element is invalid with respect to ApiUserOrPetOrArrayString
+        */
+        @Throws(IOException::class)
+        fun validateJsonElement(jsonElement: JsonElement?) {
+            var match = 0
+            val errorMessages = ArrayList<String>()
+            // validate the json string with ApiUser
+            try {
+                // validate the JSON object to see if any exception is thrown
+                ApiUser.validateJsonElement(jsonElement)
+                match++
+            } catch (e: Exception) {
+                // Validation failed, continue
+                errorMessages.add(String.format("Validation for ApiUser failed with `%s`.", e.message))
+            }
+            // validate the json string with ApiPet
+            try {
+                // validate the JSON object to see if any exception is thrown
+                ApiPet.validateJsonElement(jsonElement)
+                match++
+            } catch (e: Exception) {
+                // Validation failed, continue
+                errorMessages.add(String.format("Validation for ApiPet failed with `%s`.", e.message))
+            }
+            // validate the json string with kotlin.collections.List<kotlin.String>
+            try {
+                // validate the JSON object to see if any exception is thrown
+                require(jsonElement!!.isJsonArray) {
+                    String.format("Expected json element to be a array type in the JSON string but got `%s`", jsonElement.toString())
+                }
+
+                // validate array items
+                for(element in jsonElement!!.getAsJsonArray()) {
+                    require(element.getAsJsonPrimitive().isString) {
+                        String.format("Expected array items to be of type String in the JSON string but got `%s`", jsonElement.toString())
+                    }
+                }
+                match++
+            } catch (e: Exception) {
+                // Validation failed, continue
+                errorMessages.add(String.format("Validation for kotlin.collections.List<kotlin.String> failed with `%s`.", e.message))
+            }
+
+            if (match != 1) {
+                throw IOException(String.format("Failed validation for ApiUserOrPetOrArrayString: %d classes match result, expected 1. Detailed failure message for oneOf schemas: %s. JSON: %s", match, errorMessages, jsonElement.toString()))
+            }
+        }
+    }
 }