diff --git a/library/ecp_curves.c b/library/ecp_curves.c
index f5afe44..db6ad3c 100644
--- a/library/ecp_curves.c
+++ b/library/ecp_curves.c
@@ -1264,7 +1264,7 @@
     int ret;
     size_t i;
     mpi M, R;
-    t_uint Mp[P_KOBLITZ_MAX + P_KOBLITZ_R];
+    t_uint Mp[P_KOBLITZ_MAX + P_KOBLITZ_R + 1];
 
     if( N->n < p_limbs )
         return( 0 );
@@ -1286,7 +1286,7 @@
     memcpy( Mp, N->p + p_limbs - adjust, M.n * sizeof( t_uint ) );
     if( shift != 0 )
         MPI_CHK( mpi_shift_r( &M, shift ) );
-    M.n += R.n - adjust; /* Make room for multiplication by R */
+    M.n += R.n; /* Make room for multiplication by R */
 
     /* N = A0 */
     if( mask != 0 )
@@ -1308,7 +1308,7 @@
     memcpy( Mp, N->p + p_limbs - adjust, M.n * sizeof( t_uint ) );
     if( shift != 0 )
         MPI_CHK( mpi_shift_r( &M, shift ) );
-    M.n += R.n - adjust; /* Make room for multiplication by R */
+    M.n += R.n; /* Make room for multiplication by R */
 
     /* N = A0 */
     if( mask != 0 )