diff --git a/src/graphblas/system/cusp/detail/assign.inl b/src/graphblas/system/cusp/detail/assign.inl
index d460d3f..77b8766 100644
--- a/src/graphblas/system/cusp/detail/assign.inl
+++ b/src/graphblas/system/cusp/detail/assign.inl
@@ -125,6 +125,8 @@ namespace backend
                 j_d.begin(),
                 temp.column_indices.begin());
 
+            temp.sort_by_row_and_column();
+
             //remove entries from c:
             auto end_diff = thrust::set_difference_by_key(
                     thrust::make_zip_iterator(thrust::make_tuple(