diff --git a/library/bignum.c b/library/bignum.c
index 886429206..25fe8beeb 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -1881,6 +1881,7 @@ int mbedtls_mpi_fill_random( mbedtls_mpi *X, size_t size,
     MBEDTLS_MPI_CHK( mbedtls_mpi_read_binary( X, buf, size ) );
 
 cleanup:
+    mbedtls_zeroize( buf, sizeof( buf ) );
     return( ret );
 }