diff --git a/src/lib/monitor-adapter.js b/src/lib/monitor-adapter.js
index 3f9b199d7fd175187498661c7b110c761e9ebdbf..be0b1db7199cca86045d5b200b7c7cf0d9a6cb9c 100644
--- a/src/lib/monitor-adapter.js
+++ b/src/lib/monitor-adapter.js
@@ -15,6 +15,8 @@ const isUndefined = a => typeof a === 'undefined';
  * @return {object} The adapted monitor with label and category
  */
 export default function ({id, spriteName, opcode, params, value, vm}) {
+    // Extension monitors get their labels from the Runtime through `getLabelForOpcode`.
+    // Other monitors' labels are hard-coded in `OpcodeLabels`.
     let {label, category, labelFn} = (vm && vm.runtime.getLabelForOpcode(opcode)) || OpcodeLabels(opcode);
 
     // Use labelFn if provided for dynamic labelling (e.g. variables)