diff --git a/new_examples/synchronization/histogram_10_6th_safe_parallel_private.cpp b/new_examples/synchronization/histogram_10_6th_safe_parallel_private.cpp
index b2be74d170..763a3d0b58 100644
--- a/new_examples/synchronization/histogram_10_6th_safe_parallel_private.cpp
+++ b/new_examples/synchronization/histogram_10_6th_safe_parallel_private.cpp
@@ -63,7 +63,7 @@ int main(int argc, char** argv) {
               });
   //Sequential reduction of the private histograms
   vector_t hist_p(num_bins);
-  priv_h.combine_each([&](vector_t a)
+  priv_h.combine_each([&](vector_t& a)
     { // for each priv histogram a
       std::transform(hist_p.begin(),    // source 1 begin
                      hist_p.end(),      // source 1 end