diff --git a/resources/idlharness.js b/resources/idlharness.js
index 6620b765808d46..c65a3a476976a9 100644
--- a/resources/idlharness.js
+++ b/resources/idlharness.js
@@ -855,6 +855,8 @@ IdlArray.prototype.collapse_partials = function()
         {
             // Special-case "Exposed". Must be a subset of original interface's exposure.
             // Exposed on a partial is the equivalent of having the same Exposed on all nested members.
+            // See https://github.com/heycam/webidl/issues/154 for discrepency between Exposed and
+            // other extended attributes on partial interfaces.
             const exposureAttr = parsed_idl.extAttrs.find(a => a.name === "Exposed");
             if (exposureAttr) {
                 if (!parsed_idl.untested) {