diff --git a/modules/openapi-generator/src/main/resources/kotlin-client/libraries/jvm-okhttp/infrastructure/ApiClient.kt.mustache b/modules/openapi-generator/src/main/resources/kotlin-client/libraries/jvm-okhttp/infrastructure/ApiClient.kt.mustache
index 650703ba5e..36f6ce3288 100644
--- a/modules/openapi-generator/src/main/resources/kotlin-client/libraries/jvm-okhttp/infrastructure/ApiClient.kt.mustache
+++ b/modules/openapi-generator/src/main/resources/kotlin-client/libraries/jvm-okhttp/infrastructure/ApiClient.kt.mustache
@@ -288,14 +288,14 @@ import com.squareup.moshi.adapter
                     requestConfig.headers["{{keyParamName}}"] = apiKeyPrefix["{{keyParamName}}"]!! + " " + apiKey["{{keyParamName}}"]!!
                     {{/isKeyInHeader}}
                     {{#isKeyInQuery}}
-                    requestConfig.query["{{keyParamName}}"] = apiKeyPrefix["{{keyParamName}}"]!! + " " + apiKey["{{keyParamName}}"]!!
+                    requestConfig.query["{{keyParamName}}"] = listOf(apiKeyPrefix["{{keyParamName}}"]!! + " " + apiKey["{{keyParamName}}"]!!)
                     {{/isKeyInQuery}}
                 } else {
                     {{#isKeyInHeader}}
                     requestConfig.headers["{{keyParamName}}"] = apiKey["{{keyParamName}}"]!!
                     {{/isKeyInHeader}}
                     {{#isKeyInQuery}}
-                    requestConfig.query["{{keyParamName}}"] = apiKey["{{keyParamName}}"]!!
+                    requestConfig.query["{{keyParamName}}"] = listOf(apiKey["{{keyParamName}}"]!!)
                     {{/isKeyInQuery}}
                 }
             }