diff --git a/drama/src/rev-mc.c b/drama/src/rev-mc.c
index f3bf53d..96b9e40 100644
--- a/drama/src/rev-mc.c
+++ b/drama/src/rev-mc.c
@@ -328,7 +328,8 @@ find_row_mask(std::vector<set_t> &sets,
     std::vector<std::thread> workers;
     auto thread_num = std::thread::hardware_concurrency();
     if (thread_num > 2) { thread_num -= 2; }
-    const uint64_t step = (last_mask - row_mask) / thread_num;
+    uint64_t step = 0;
+    for (uint64_t i = row_mask; i < last_mask; ++step) { i = next_bit_permutation(i); }
 
     for (int i = 0; i < thread_num; ++i) {
         workers.emplace_back([&] {