diff --git a/README.md b/README.md
index 8920091..4647d47 100644
--- a/README.md
+++ b/README.md
@@ -286,6 +286,10 @@ You can use following example configuration in `package.json`:
   "test": "mocha --reporter json > test-results.json"
 }
 ```
+
+Test processing might fail if any of your tests writes anything on standard output.
+Mocha unfortunately doesn't have option to store `json` output directly to file and we have to rely on redirecting its standard output.
+There is a work in progress to fix it: [mocha#4607](https://github.com/mochajs/mocha/pull/4607)
 </details>
 
 ## GitHub limitations