diff --git a/modules/openapi-generator/src/main/resources/kotlin-client/libraries/jvm-retrofit2/api.mustache b/modules/openapi-generator/src/main/resources/kotlin-client/libraries/jvm-retrofit2/api.mustache
index d99122333d6..4381539414c 100644
--- a/modules/openapi-generator/src/main/resources/kotlin-client/libraries/jvm-retrofit2/api.mustache
+++ b/modules/openapi-generator/src/main/resources/kotlin-client/libraries/jvm-retrofit2/api.mustache
@@ -69,7 +69,7 @@ import okhttp3.MultipartBody
 
 {{/isMultipart}}
 {{/x-kotlin-multipart-import}}
-interface {{classname}} {
+{{#nonPublicApi}}internal {{/nonPublicApi}}interface {{classname}} {
     {{#operation}}
     {{#allParams}}
     {{#isEnum}}