diff --git a/drama/src/rev-mc.c b/drama/src/rev-mc.c
index 70e1ac6..c5bba1f 100644
--- a/drama/src/rev-mc.c
+++ b/drama/src/rev-mc.c
@@ -320,6 +320,7 @@ find_row_mask(std::vector<set_t> &sets,
 
     std::atomic_bool found{false};
     std::mutex lock;
+    const uint64_t step = 10000;
 
     // while (row_mask < last_mask) {
     //     row_mask = next_bit_permutation(row_mask);
@@ -330,19 +331,18 @@ find_row_mask(std::vector<set_t> &sets,
     if (thread_num > 2) { thread_num -= 2; }
     for (int i = 0; i < thread_num; ++i) {
         workers.emplace_back([&] {
-            std::vector<uint64_t> masks;
             while (!found) {
+                uint64_t cur_mask = last_mask;
                 {
-                    masks.clear();
                     std::lock_guard<std::mutex> _(lock);
-                    for (int i = 0; i < 10000 && row_mask < last_mask; ++i) {
-                        masks.push_back(row_mask);
+                    if (row_mask >= last_mask) { break; }
+                    cur_mask = row_mask;
+                    for (int i = 0; i < step && row_mask < last_mask; ++i) {
                         row_mask = next_bit_permutation(row_mask);
                     }
-                    if (row_mask >= last_mask) { break; }
                 }
 
-                for (const auto &cur_mask : masks) {
+                for (int i = 0; i < step && cur_mask < last_mask; ++i) {
                     if (resolve(cur_mask, found)) {
                         std::lock_guard<std::mutex> _(lock);
                         if (!found.exchange(true)) {