diff --git a/packages/block-editor/src/components/block-list/use-in-between-inserter.js b/packages/block-editor/src/components/block-list/use-in-between-inserter.js
index d2b75ffa97f402..68fa8628c54c72 100644
--- a/packages/block-editor/src/components/block-list/use-in-between-inserter.js
+++ b/packages/block-editor/src/components/block-list/use-in-between-inserter.js
@@ -40,6 +40,8 @@ export function useInBetweenInserter() {
 			}
 
 			function onMouseMove( event ) {
+				// openRef is the reference to the insertion point between blocks.
+				// If the reference is not set or the insertion point is already open, return.
 				if ( openRef === undefined || openRef.current ) {
 					return;
 				}