diff --git a/openapi/openapi.yaml b/openapi/openapi.yaml
index 09db5506..b6f0ea9d 100644
--- a/openapi/openapi.yaml
+++ b/openapi/openapi.yaml
@@ -55,7 +55,7 @@ paths:
         '200':
           description: successful operation
           content:
-            text/plain:
+            text/plain; charset=utf-8:
               schema:
                 type: string
                 example: ok