diff --git a/openapi/openapi.yaml b/openapi/openapi.yaml
index 3c412bb6..1a678a12 100644
--- a/openapi/openapi.yaml
+++ b/openapi/openapi.yaml
@@ -54,7 +54,7 @@ paths:
         '200':
           description: successful operation
           content:
-            text/plain:
+            text/plain; charset=utf-8:
               schema:
                 type: string
                 example: ok