diff --git a/drama/src/rev-mc.c b/drama/src/rev-mc.c
index d448aae..3f225f4 100644
--- a/drama/src/rev-mc.c
+++ b/drama/src/rev-mc.c
@@ -370,15 +370,16 @@ find_row_mask(std::vector<set_t> &sets,
 
                     step_count -= std::min(step_count, step / 10);
 
+                    // my is new
                     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 + step_count) {
                             g_base_pos = my_pos;
                             row_mask   = cur_mask;
                         }
-                    } else {
+                    } else if (g_base_pos.load(std::memory_order_relaxed) <= my_pos) {
                         std::lock_guard<std::mutex> _(lock);
-                        if (g_base_pos + step_count <= my_pos) {
+                        if (g_base_pos <= my_pos) {
                             cur_mask   = row_mask;
                             step_count = my_pos - g_base_pos;
                         }