diff --git a/drama/src/rev-mc.c b/drama/src/rev-mc.c
index 7d7215a..876ccbf 100644
--- a/drama/src/rev-mc.c
+++ b/drama/src/rev-mc.c
@@ -346,14 +346,15 @@ find_row_mask(std::vector<set_t> &sets,
     for (int i = 0; i < thread_num; ++i) {
         workers.emplace_back([&] {
             while (!found) {
-                uint64_t cur_mask   = last_mask;
+                uint64_t cur_mask   = 0;
                 uint64_t step_count = 0;
                 uint64_t my_pos     = 0;
                 {
                     std::lock_guard<std::mutex> _(lock);
-                    if (row_mask >= last_mask || found) { break; }
-                    cur_mask   = row_mask;
+                    if (row_mask >= last_mask || found) { return; }
                     step_count = g_cur_pos - g_base_pos;
+
+                    cur_mask   = row_mask;
                     my_pos     = g_cur_pos.fetch_add(step);
                 }
                 while (cur_mask < last_mask && step_count > 0 && !found.load(std::memory_order_relaxed)) {
@@ -369,15 +370,15 @@ find_row_mask(std::vector<set_t> &sets,
 
                     step_count -= std::min(step_count, step);
 
-                    if (my_pos > g_base_pos.load(std::memory_order_relaxed)) {
+                    if (my_pos > g_base_pos.load(std::memory_order_relaxed) + step_count) {
                         std::lock_guard<std::mutex> _(lock);
-                        if (my_pos > g_base_pos) {
+                        if (my_pos > g_base_pos + step_count) {
                             g_base_pos = my_pos;
                             row_mask   = cur_mask;
                         }
-                    } else if (g_base_pos.load(std::memory_order_relaxed) < my_pos) {
+                    } else {
                         std::lock_guard<std::mutex> _(lock);
-                        if (g_base_pos <= my_pos) {
+                        if (g_base_pos + step_count <= my_pos) {
                             cur_mask   = row_mask;
                             step_count = my_pos - g_base_pos;
                         }