avoid warnings
diff --git a/sampling/test/var_opt_union_test.cpp b/sampling/test/var_opt_union_test.cpp
index f9b653b..964e869 100644
--- a/sampling/test/var_opt_union_test.cpp
+++ b/sampling/test/var_opt_union_test.cpp
@@ -40,8 +40,8 @@
 
 static var_opt_sketch<int> create_unweighted_sketch(uint32_t k, uint64_t n) {
   var_opt_sketch<int> sk(k);
-  for (int i = 0; i < n; ++i) {
-    sk.update(i, 1.0);
+  for (uint64_t i = 0; i < n; ++i) {
+    sk.update(static_cast<int>(i), 1.0);
   }
   return sk;
 }
@@ -193,7 +193,7 @@
   u.update(sk2);
 
   var_opt_sketch<int> result = u.get_result();
-  REQUIRE(result.get_n() == 2 * n);
+  REQUIRE(result.get_n() == 2ULL * n);
   REQUIRE(result.get_k() == k);
 }