diff --git a/library/bignum.c b/library/bignum.c
index f5130b406..0a9560734 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -1884,6 +1884,7 @@ int mpi_fill_random( mpi *X, size_t size,
     MPI_CHK( mpi_read_binary( X, buf, size ) );
 
 cleanup:
+    polarssl_zeroize( buf, sizeof( buf ) );
     return( ret );
 }