diff --git a/runtime/tools/heapsnapshot/README.md b/runtime/tools/heapsnapshot/README.md
index aac6920a5e6..3bac41b22fc 100644
--- a/runtime/tools/heapsnapshot/README.md
+++ b/runtime/tools/heapsnapshot/README.md
@@ -13,6 +13,8 @@ heapsnapshot.
 
 ### Programmatically
 
+Note: enabled for debug and release Dart build modes, but not for product mode.
+
 It's possible to programmatically dump a heapsnapshot to a file by using a
 `dart:developer` API:
 ```