diff --git a/core/privc3/fixedpoint_tensor_imp.h b/core/privc3/fixedpoint_tensor_imp.h
index e92bd6840c8789e1ce6558bf51986313ed788897..adf660a7d55d2282b65b35fc41b30d0101513115 100644
--- a/core/privc3/fixedpoint_tensor_imp.h
+++ b/core/privc3/fixedpoint_tensor_imp.h
@@ -211,10 +211,10 @@ void FixedPointTensor<T, N>::truncate(const FixedPointTensor<T, N>* op,
 
 #else // use truncate3
 
-// Protocol. `truncate3`
+// Protocol. `truncate3` (illustrated for data type T = int64_t)
 // motivation:
 // truncates in aby3 may cause msb error with small probability
-// the reason is that before rishft op, its masked value e.g., x' - r' may overflow in int64
+// the reason is that before rishft op, its masked value e.g., x' - r' may overflow in int64_t
 // so that, in `truncate3`, we limit r' in (-2^62, 2^62) to avoid the problem.
 
 // notice:
@@ -245,17 +245,14 @@ void FixedPointTensor<T, N>::truncate(const FixedPointTensor<T, N>* op,
             temp.emplace_back(
                 tensor_factory()->template create<T>(op->shape()));
         }
-        // r',  contraint in (-2^62, 2^62)
+        // r',  contraint in (constraint_low, contraint_upper)
         aby3_ctx()->template gen_random_private(*temp[0]);
-        int64_t contraint_upper = ~((uint64_t) 1 << 62);
-        int64_t contraint_low = (uint64_t) 1 << 62;
+        T contraint_upper = (T) 1 << (sizeof(T) * 8 - 2);
+        T contraint_low = - contraint_upper;
         std::for_each(temp[0]->data(), temp[0]->data() + temp[0]->numel(),
                       [&contraint_upper, &contraint_low] (T& a) {
-                          // contraint -2^62 < a < 2^62
-                          if (a >= 0) {
-                              a &= contraint_upper;
-                          } else {
-                              a |= contraint_low;
+                          while ((a > contraint_upper || a < contraint_low)) {
+                              a = aby3_ctx()->template gen_random_private<T>();
                           }
                       });