diff --git a/include/mbedtls/bignum.h b/include/mbedtls/bignum.h
index e938232..3274422 100644
--- a/include/mbedtls/bignum.h
+++ b/include/mbedtls/bignum.h
@@ -894,6 +894,8 @@
  *
  * \return         \c 0 if successful.
  * \return         #MBEDTLS_ERR_MPI_ALLOC_FAILED if a memory allocation failed.
+ * \return         #MBEDTLS_ERR_MPI_BAD_INPUT_DATA if \p min or \p N is invalid
+ *                 or if they are incompatible.
  * \return         Another negative error code on failure.
  */
 int mbedtls_mpi_random( mbedtls_mpi *X,