diff --git a/lib/libmbedtls/mbedtls/library/bignum.c b/lib/libmbedtls/mbedtls/library/bignum.c
index 4c1840a..e947a1c 100644
--- a/lib/libmbedtls/mbedtls/library/bignum.c
+++ b/lib/libmbedtls/mbedtls/library/bignum.c
@@ -1789,7 +1789,7 @@
     size_t bufsize, nbits;
     mbedtls_mpi_uint ei, mm, state;
     mbedtls_mpi RR, T, Apos;
-    mbedtls_mpi *W;
+    mbedtls_mpi *W = NULL;
     const size_t array_size_W = 2 << MBEDTLS_MPI_WINDOW_SIZE;
     int neg;
 
@@ -1804,19 +1804,12 @@
     if( mbedtls_mpi_cmp_int( E, 0 ) < 0 )
         return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
 
-    W = mempool_alloc( mbedtls_mpi_mempool,
-                       sizeof( mbedtls_mpi ) * array_size_W );
-    if( W == NULL )
-        return( MBEDTLS_ERR_MPI_ALLOC_FAILED );
-
     /*
      * Init temps and window size
      */
     mbedtls_mpi_montg_init( &mm, N );
     mbedtls_mpi_init_mempool( &RR ); mbedtls_mpi_init_mempool( &T );
     mbedtls_mpi_init_mempool( &Apos );
-    for( i = 0; i < array_size_W; i++ )
-        mbedtls_mpi_init_mempool( W + i );
 
     i = mbedtls_mpi_bitlen( E );
 
@@ -1828,7 +1821,7 @@
 
     j = N->n + 1;
     MBEDTLS_MPI_CHK( mbedtls_mpi_grow( X, j ) );
-    MBEDTLS_MPI_CHK( mbedtls_mpi_grow( &W[1],  j ) );
+
     MBEDTLS_MPI_CHK( mbedtls_mpi_grow( &T, j * 2 ) );
 
     /*
@@ -1857,6 +1850,16 @@
     else
         memcpy( &RR, _RR, sizeof( mbedtls_mpi ) );
 
+    W = mempool_alloc( mbedtls_mpi_mempool,
+                       sizeof( mbedtls_mpi ) * array_size_W );
+    if( W == NULL ) {
+        ret = MBEDTLS_ERR_MPI_ALLOC_FAILED;
+        goto cleanup;
+    }
+    for( i = 0; i < array_size_W; i++ )
+        mbedtls_mpi_init_mempool( W + i );
+    MBEDTLS_MPI_CHK( mbedtls_mpi_grow( &W[1],  j ) );
+
     /*
      * W[1] = A * R^2 * R^-1 mod N = A * R mod N
      */
@@ -1988,8 +1991,9 @@
 
 cleanup:
 
-    for( i = 0; i < array_size_W; i++ )
-        mbedtls_mpi_free( W + i );
+    if( W )
+        for( i = 0; i < array_size_W; i++ )
+            mbedtls_mpi_free( W + i );
     mempool_free( mbedtls_mpi_mempool , W );
 
     mbedtls_mpi_free( &T ); mbedtls_mpi_free( &Apos );