diff --git a/library/bignum.c b/library/bignum.c
index 3fa6a3b..de61952 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -1569,6 +1569,7 @@
  *                      (T->n >= 2 * N->n + 1).
  *                      Its initial content is unused and
  *                      its final content is indeterminate.
+ *                      It does not get reallocated.
  */
 static void mpi_montmul( mbedtls_mpi *A, const mbedtls_mpi *B,
                          const mbedtls_mpi *N, mbedtls_mpi_uint mm,