diff --git a/modules/swagger-codegen/src/main/resources/kotlin-client/api.mustache b/modules/swagger-codegen/src/main/resources/kotlin-client/api.mustache
index 9b78ac8f2cb..11ecf02624a 100644
--- a/modules/swagger-codegen/src/main/resources/kotlin-client/api.mustache
+++ b/modules/swagger-codegen/src/main/resources/kotlin-client/api.mustache
@@ -19,8 +19,8 @@ class {{classname}}(basePath: kotlin.String = "{{{basePath}}}") : ApiClient(base
     @Suppress("UNCHECKED_CAST"){{/returnType}}
     fun {{operationId}}({{#allParams}}{{paramName}}: {{{dataType}}}{{#hasMore}}, {{/hasMore}}{{/allParams}}) : {{#returnType}}{{{returnType}}}{{/returnType}}{{^returnType}}Unit{{/returnType}} {
         val localVariableBody: kotlin.Any? = {{#hasBodyParam}}{{#bodyParams}}{{paramName}}{{/bodyParams}}{{/hasBodyParam}}{{^hasBodyParam}}{{^hasFormParams}}null{{/hasFormParams}}{{#hasFormParams}}mapOf({{#formParams}}"{{{baseName}}}" to "${{paramName}}"{{#hasMore}}, {{/hasMore}}{{/formParams}}){{/hasFormParams}}{{/hasBodyParam}}
-        val localVariableQuery: MultiValueMap = {{^hasQueryParams}}mapOf(){{/hasQueryParams}}{{#hasQueryParams}}mapOf({{#queryParams}}"{{paramName}}" to {{#isContainer}}toMultiValue({{paramName}}.toList(), "{{collectionFormat}}"){{/isContainer}}{{^isContainer}}listOf("${{paramName}}"){{/isContainer}}{{#hasMore}}, {{/hasMore}}{{/queryParams}}){{/hasQueryParams}}
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf({{#hasFormParams}}"Content-Type" to "multipart/form-data"{{/hasFormParams}}{{^hasHeaderParams}}){{/hasHeaderParams}}{{#hasHeaderParams}}{{#hasFormParams}}, {{/hasFormParams}}{{#headerParams}}"{{paramName}}" to {{#isContainer}}{{paramName}}.joinToString(separator = collectionDelimiter("{{collectionFormat}}"){{/isContainer}}{{^isContainer}}{{paramName}}{{/isContainer}}{{#hasMore}}, {{/hasMore}}{{/headerParams}}){{/hasHeaderParams}}
+        val localVariableQuery: MultiValueMap = {{^hasQueryParams}}mapOf(){{/hasQueryParams}}{{#hasQueryParams}}mapOf({{#queryParams}}"{{baseName}}" to {{#isContainer}}toMultiValue({{paramName}}.toList(), "{{collectionFormat}}"){{/isContainer}}{{^isContainer}}listOf("${{paramName}}"){{/isContainer}}{{#hasMore}}, {{/hasMore}}{{/queryParams}}){{/hasQueryParams}}
+        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf({{#hasFormParams}}"Content-Type" to "multipart/form-data"{{/hasFormParams}}{{^hasHeaderParams}}){{/hasHeaderParams}}{{#hasHeaderParams}}{{#hasFormParams}}, {{/hasFormParams}}{{#headerParams}}"{{baseName}}" to {{#isContainer}}{{paramName}}.joinToString(separator = collectionDelimiter("{{collectionFormat}}"){{/isContainer}}{{^isContainer}}{{paramName}}{{/isContainer}}{{#hasMore}}, {{/hasMore}}{{/headerParams}}){{/hasHeaderParams}}
         val localVariableConfig = RequestConfig(
             RequestMethod.{{httpMethod}},
             "{{path}}"{{#pathParams}}.replace("{"+"{{baseName}}"+"}", "${{paramName}}"){{/pathParams}},
diff --git a/samples/client/petstore/kotlin/.swagger-codegen/VERSION b/samples/client/petstore/kotlin/.swagger-codegen/VERSION
index f9f7450d135..a6254504e40 100644
--- a/samples/client/petstore/kotlin/.swagger-codegen/VERSION
+++ b/samples/client/petstore/kotlin/.swagger-codegen/VERSION
@@ -1 +1 @@
-2.3.0-SNAPSHOT
\ No newline at end of file
+2.3.1
\ No newline at end of file
diff --git a/samples/client/petstore/kotlin/src/main/kotlin/io/swagger/client/apis/PetApi.kt b/samples/client/petstore/kotlin/src/main/kotlin/io/swagger/client/apis/PetApi.kt
index c716883b340..5d6d2f187eb 100644
--- a/samples/client/petstore/kotlin/src/main/kotlin/io/swagger/client/apis/PetApi.kt
+++ b/samples/client/petstore/kotlin/src/main/kotlin/io/swagger/client/apis/PetApi.kt
@@ -59,7 +59,7 @@ class PetApi(basePath: kotlin.String = "http://petstore.swagger.io/v2") : ApiCli
     fun deletePet(petId: kotlin.Long, apiKey: kotlin.String) : Unit {
         val localVariableBody: kotlin.Any? = null
         val localVariableQuery: MultiValueMap = mapOf()
-        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf("apiKey" to apiKey)
+        val localVariableHeaders: kotlin.collections.Map<kotlin.String,kotlin.String> = mapOf("api_key" to apiKey)
         val localVariableConfig = RequestConfig(
             RequestMethod.DELETE,
             "/pet/{petId}".replace("{"+"petId"+"}", "$petId"),