diff --git a/task2/include/quicksort_mt.h b/task2/include/quicksort_mt.h
index f918818..947b494 100644
--- a/task2/include/quicksort_mt.h
+++ b/task2/include/quicksort_mt.h
@@ -3,6 +3,7 @@
 #include <thread>
 #include <mutex>
 #include <functional>
+#include <assert.h>
 
 template<typename T>
 class QuickSorterMT {
@@ -49,8 +50,7 @@ private:
                 return;
             }
         }
-
-        auto pivot = data[std::distance(data.begin(), data.end()) / 2];
+        auto pivot = *std::next(data.begin(), std::distance(data.begin(), data.end()) / 2);
 
         auto m1 = std::partition(data.begin(), data.end(), [pivot, this](const auto &em) {
             return this->cmp(em, pivot);
@@ -60,8 +60,10 @@ private:
             return !(this->cmp(em, pivot));
         });
 
+        assert((m1 - data.begin()) <= data.size());
+        assert((m2 - data.begin()) <= data.size());
         auto left = data.subspan(0, m1 - data.begin());
-        auto right = data.subspan(m2 - data.begin(), data.size());
+        auto right = data.subspan(m2 - data.begin());
 
         if (depth < mdepth) {
             std::thread left_thread([&]() { qsort(left, depth + 1, mdepth); });