diff --git a/pageserver/src/tenant/timeline.rs b/pageserver/src/tenant/timeline.rs
index 67ea94042b..681e33ee5f 100644
--- a/pageserver/src/tenant/timeline.rs
+++ b/pageserver/src/tenant/timeline.rs
@@ -3048,7 +3048,10 @@ impl Timeline {
                 image_layers.push(image_layer);
             }
         }
-        // All wanted layers are taken in account by time_for_new_image_layer
+        // All wanted layers are taken in account by time_for_new_image_layer.
+        // The watend_image_layers could get updated out of turn and we could
+        // clear something which hasn't been looked at all. This is fine, because
+        // next gc round any wanted would get added back in.
         *self.wanted_image_layers.lock().unwrap() = None;
 
         // Sync the new layer to disk before adding it to the layer map, to make sure