Clarify parameter documentation
Signed-off-by: Felix Conway <felix.conway@arm.com>
diff --git a/include/mbedtls/bignum.h b/include/mbedtls/bignum.h
index ed0c4e7..c67d653 100644
--- a/include/mbedtls/bignum.h
+++ b/include/mbedtls/bignum.h
@@ -993,8 +993,9 @@
* to an initialized MPI. This value can be negative, in which
* case a positive answer will still be returned in \p X.
* \param N The base of the modular inversion. This must point to an
- * initialized MPI. If this points to the same MPI as \p X,
- * then the value returned in \p X will be incorrect.
+ * initialized MPI and be greater than one. If this points to
+ * the same MPI as \p X, then the value returned in \p X will
+ * be incorrect.
*
* \return \c 0 if successful.
* \return #MBEDTLS_ERR_MPI_ALLOC_FAILED if a memory allocation failed.