diff --git a/src/libslic3r/Thread.cpp b/src/libslic3r/Thread.cpp
index 106da4a781..4e7bd073a2 100644
--- a/src/libslic3r/Thread.cpp
+++ b/src/libslic3r/Thread.cpp
@@ -208,7 +208,7 @@ void name_tbb_thread_pool_threads_set_locale()
 	nthreads = 1;
 #endif
 
-	std::atomic<size_t>		nthreads_running(0);
+	size_t                  nthreads_running(0);
 	std::condition_variable cv;
 	std::mutex				cv_m;
 	auto					master_thread_id = std::this_thread::get_id();
@@ -216,13 +216,13 @@ void name_tbb_thread_pool_threads_set_locale()
         tbb::blocked_range<size_t>(0, nthreads, 1),
         [&nthreads_running, nthreads, &master_thread_id, &cv, &cv_m](const tbb::blocked_range<size_t> &range) {
         	assert(range.begin() + 1 == range.end());
-        	if (nthreads_running.fetch_add(1) + 1 == nthreads) {
+			if (std::unique_lock<std::mutex> lk(cv_m);  ++nthreads_running == nthreads) {
+				lk.unlock();
         		// All threads are spinning.
         		// Wake them up.
     			cv.notify_all();
         	} else {
         		// Wait for the last thread to wake the others.
-				std::unique_lock<std::mutex> lk(cv_m);
 			    cv.wait(lk, [&nthreads_running, nthreads]{return nthreads_running == nthreads;});
         	}
         	auto thread_id = std::this_thread::get_id();