diff --git a/doc/requirements-and-limitations.md b/doc/requirements-and-limitations.md
index ae577f2..9129d42 100644
--- a/doc/requirements-and-limitations.md
+++ b/doc/requirements-and-limitations.md
@@ -32,3 +32,4 @@ The `SUPER` privilege is required for `STOP SLAVE`, `START SLAVE` operations. Th
   - We began working towards removing this limitation. See tracking issue: https://github.com/github/gh-ost/issues/163
 - Multisource is not supported when migrating via replica. It _should_ work (but never tested) when connecting directly to master (`--allow-on-master`)
 - Master-master setup is only supported in active-passive setup. Active-active (where table is being written to on both masters concurrently) is unsupported. It may be supported in the future.
+- If you have en `enum` field as part of your migration key (typically the `PRIMARY KEY`), migration performance will be degraded and potentially bad. [Read more](https://github.com/github/gh-ost/pull/277#issuecomment-254811520)