diff --git a/include/mbedtls/aes.h b/include/mbedtls/aes.h
index a8d430614..6c75f77c1 100644
--- a/include/mbedtls/aes.h
+++ b/include/mbedtls/aes.h
@@ -77,7 +77,9 @@ typedef struct mbedtls_aes_context {
     size_t MBEDTLS_PRIVATE(rk_offset);           /*!< The offset in array elements to AES
                                                     round keys in the buffer. */
 #if defined(MBEDTLS_AES_ONLY_128_BIT_KEY_LENGTH) && !defined(MBEDTLS_PADLOCK_C)
-    uint32_t MBEDTLS_PRIVATE(buf)[44];
+    uint32_t MBEDTLS_PRIVATE(buf)[44];           /*!< Aligned data buffer to hold
+                                                    round keys in the 128-bit case for
+                                                    10 rounds calculation. */
 #else
     uint32_t MBEDTLS_PRIVATE(buf)[68];           /*!< Unaligned data buffer. This buffer can
                                                     hold 32 extra Bytes, which can be used for