diff --git a/components/esp32/include/rom/aes.h b/components/esp32/include/rom/aes.h
index 9fd0e5baea..2f058f1c25 100644
--- a/components/esp32/include/rom/aes.h
+++ b/components/esp32/include/rom/aes.h
@@ -1,3 +1,10 @@
+/*
+  ROM functions for hardware AES support.
+
+  It is not recommended to use these functions directly,
+  use the wrapper functions in hwcrypto/aes.h instead.
+
+ */
 // Copyright 2015-2016 Espressif Systems (Shanghai) PTE LTD
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
diff --git a/components/esp32/include/rom/bigint.h b/components/esp32/include/rom/bigint.h
index 461469cacd..624336695b 100644
--- a/components/esp32/include/rom/bigint.h
+++ b/components/esp32/include/rom/bigint.h
@@ -1,3 +1,10 @@
+/*
+  ROM functions for hardware bigint support.
+
+  It is not recommended to use these functions directly,
+  use the wrapper functions in hwcrypto/mpi.h instead.
+
+ */
 // Copyright 2015-2016 Espressif Systems (Shanghai) PTE LTD
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
diff --git a/components/esp32/include/rom/sha.h b/components/esp32/include/rom/sha.h
index a5536bd3ba..b35faa9a07 100644
--- a/components/esp32/include/rom/sha.h
+++ b/components/esp32/include/rom/sha.h
@@ -1,3 +1,10 @@
+/*
+  ROM functions for hardware SHA support.
+
+  It is not recommended to use these functions directly,
+  use the wrapper functions in hwcrypto/sha.h instead.
+
+ */
 // Copyright 2015-2016 Espressif Systems (Shanghai) PTE LTD
 //
 // Licensed under the Apache License, Version 2.0 (the "License");