diff --git a/include/mbedtls/ssl_internal.h b/include/mbedtls/ssl_internal.h
index 61ac464179..6f7b458238 100644
--- a/include/mbedtls/ssl_internal.h
+++ b/include/mbedtls/ssl_internal.h
@@ -146,6 +146,7 @@
 #define MBEDTLS_SSL_COMPRESSION_ADD             0
 #endif
 
+/* This macro determines whether CBC is supported. */
 #if defined(MBEDTLS_CIPHER_MODE_CBC) &&                               \
     ( defined(MBEDTLS_AES_C)      ||                                  \
       defined(MBEDTLS_CAMELLIA_C) ||                                  \
@@ -154,6 +155,8 @@
 #define MBEDTLS_SSL_SOME_SUITES_USE_CBC
 #endif
 
+/* This macro determines whether the CBC construct used in TLS 1.0-1.2 (as
+ * opposed to the very different CBC construct used in SSLv3) is supported. */
 #if defined(MBEDTLS_SSL_SOME_SUITES_USE_CBC) && \
     ( defined(MBEDTLS_SSL_PROTO_TLS1) ||        \
       defined(MBEDTLS_SSL_PROTO_TLS1_1) ||      \
@@ -161,7 +164,6 @@
 #define MBEDTLS_SSL_SOME_SUITES_USE_TLS_CBC
 #endif
 
-
 #if defined(MBEDTLS_ARC4_C) || defined(MBEDTLS_CIPHER_NULL_CIPHER) ||   \
     defined(MBEDTLS_SSL_SOME_SUITES_USE_CBC)
 #define MBEDTLS_SSL_SOME_MODES_USE_MAC