diff --git a/src/dispatcher.js b/src/dispatcher.js
index ed0350fe54..11c79f58ee 100644
--- a/src/dispatcher.js
+++ b/src/dispatcher.js
@@ -42,6 +42,9 @@ class MatrixDispatcher extends flux.Dispatcher {
     }
 }
 
+// XXX this is a big anti-pattern, and makes testing hard. Because dispatches
+// happen asynchronously, it is possible for actions dispatched in one thread
+// to arrive in another, with *hilarious* consequences.
 if (global.mxDispatcher === undefined) {
     global.mxDispatcher = new MatrixDispatcher();
 }