diff --git a/src/gperftools/malloc_extension.h b/src/gperftools/malloc_extension.h
index 689b5f1..1800266 100644
--- a/src/gperftools/malloc_extension.h
+++ b/src/gperftools/malloc_extension.h
@@ -123,6 +123,10 @@ class PERFTOOLS_DLL_DECL MallocExtension {
   // therefore be passed to "pprof". This function is equivalent to
   // ReadStackTraces. The main difference is that this function returns
   // serialized data appropriately formatted for use by the pprof tool.
+  //
+  // Since gperftools 2.8 heap samples are not de-duplicated by the
+  // library anymore.
+  //
   // NOTE: by default, tcmalloc does not do any heap sampling, and this
   //       function will always return an empty sample.  To get useful
   //       data from GetHeapSample, you must also set the environment