diff --git a/packages/material-ui/src/Unstable_TrapFocus/Unstable_TrapFocus.js b/packages/material-ui/src/Unstable_TrapFocus/Unstable_TrapFocus.js
index 255ed4492a16eb..16946a8bb6af43 100644
--- a/packages/material-ui/src/Unstable_TrapFocus/Unstable_TrapFocus.js
+++ b/packages/material-ui/src/Unstable_TrapFocus/Unstable_TrapFocus.js
@@ -26,6 +26,7 @@ function getTabIndex(node) {
   }
 
   // Browsers do not return `tabIndex` correctly for contentEditable nodes;
+  // https://bugs.chromium.org/p/chromium/issues/detail?id=661108&q=contenteditable%20tabindex&can=2
   // so if they don't have a tabindex attribute specifically set, assume it's 0.
   // in Chrome, <details/>, <audio controls/> and <video controls/> elements get a default
   //  `tabIndex` of -1 when the 'tabindex' attribute isn't specified in the DOM,