diff --git a/include/mbedtls/constant_time.h b/include/mbedtls/constant_time.h
index 01d5d9d..49bb375 100644
--- a/include/mbedtls/constant_time.h
+++ b/include/mbedtls/constant_time.h
@@ -26,16 +26,19 @@
 /** Constant-time buffer comparison without branches.
  *
  * This is equivalent to the standard memcmp function, but is likely to be
- * compiled to code using bitwise operation rather than a branch.
+ * compiled to code using bitwise operation rather than a branch, such that
+ * the time taken is constant w.r.t. the data pointed to by \p a and \p b,
+ * and w.r.t. whether \p a and \p b are equal or not. It is not constant-time
+ * w.r.t. \p n .
  *
  * This function can be used to write constant-time code by replacing branches
  * with bit operations using masks.
  *
- * \param a     Pointer to the first buffer.
- * \param b     Pointer to the second buffer.
- * \param n     The number of bytes to compare in the buffer.
+ * \param a     Pointer to the first buffer, containing at least \p n bytes. May not be NULL.
+ * \param b     Pointer to the second buffer, containing at least \p n bytes. May not be NULL.
+ * \param n     The number of bytes to compare.
  *
- * \return      Zero if the content of the two buffer is the same,
+ * \return      Zero if the contents of the two buffers are the same,
  *              otherwise non-zero.
  */
 int mbedtls_ct_memcmp(const void *a,