diff --git a/library/bignum.c b/library/bignum.c
index 4413752..f1e5443 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -1830,7 +1830,7 @@
 
     MBEDTLS_MPI_CHK( mbedtls_mpi_grow( &Z, A->n + 2 ) );
     MBEDTLS_MPI_CHK( mbedtls_mpi_lset( &Z,  0 ) );
-    MBEDTLS_MPI_CHK( mbedtls_mpi_grow( &T1, 2 ) );
+    MBEDTLS_MPI_CHK( mbedtls_mpi_grow( &T1, A->n + 2 ) );
 
     k = mbedtls_mpi_bitlen( &Y ) % biL;
     if( k < biL - 1 )