diff --git a/src/Core/AES.php b/src/Core/AES.php
index cade27d7..13c01d81 100644
--- a/src/Core/AES.php
+++ b/src/Core/AES.php
@@ -4,6 +4,8 @@
  * Bitsliced implementation of the AES block cipher.
  *
  * Based on the implementation provided by BearSSL.
+ *
+ * @internal This should only be used by sodium_compat
  */
 class ParagonIE_Sodium_Core_AES extends ParagonIE_Sodium_Core_Util
 {
diff --git a/src/Core/AES/Block.php b/src/Core/AES/Block.php
index 07615039..47ff4a69 100644
--- a/src/Core/AES/Block.php
+++ b/src/Core/AES/Block.php
@@ -4,6 +4,9 @@
     return;
 }
 
+/**
+ * @internal This should only be used by sodium_compat
+ */
 class ParagonIE_Sodium_Core_AES_Block extends SplFixedArray
 {
     /**
diff --git a/src/Core/AES/Expanded.php b/src/Core/AES/Expanded.php
index 6deb9d59..e8b84924 100644
--- a/src/Core/AES/Expanded.php
+++ b/src/Core/AES/Expanded.php
@@ -1,5 +1,8 @@
 <?php
 
+/**
+ * @internal This should only be used by sodium_compat
+ */
 class ParagonIE_Sodium_Core_AES_Expanded extends ParagonIE_Sodium_Core_AES_KeySchedule
 {
     /** @var bool $expanded */
diff --git a/src/Core/AES/KeySchedule.php b/src/Core/AES/KeySchedule.php
index 9c1b0dd9..1a5bf304 100644
--- a/src/Core/AES/KeySchedule.php
+++ b/src/Core/AES/KeySchedule.php
@@ -1,5 +1,8 @@
 <?php
 
+/**
+ * @internal This should only be used by sodium_compat
+ */
 class ParagonIE_Sodium_Core_AES_KeySchedule
 {
     /** @var array<int, int> $skey -- has size 120 */