diff --git a/listings/listing_8.3.cpp b/listings/listing_8.3.cpp
index 86b8526..e5af8d5 100644
--- a/listings/listing_8.3.cpp
+++ b/listings/listing_8.3.cpp
@@ -2,6 +2,8 @@
 #include <thread>
 #include <vector>
 #include <future>
+#include <numeric>
+#include <functional>
 template<typename Iterator,typename T>
 struct accumulate_block
 {
@@ -40,12 +42,12 @@ T parallel_accumulate(Iterator first,Iterator last,T init)
         Iterator block_end=block_start;
         std::advance(block_end,block_size);
         std::packaged_task<T(Iterator,Iterator)> task(
-            accumulate_block<Iterator,T>());
+            (accumulate_block<Iterator,T>()));
         futures[i]=task.get_future();
         threads[i]=std::thread(std::move(task),block_start,block_end);
         block_start=block_end;
     }
-    T last_result=accumulate_block<Iterator,T>(block_start,last);
+    T last_result=accumulate_block<Iterator,T>()(block_start,last);
 
     std::for_each(threads.begin(),threads.end(),
                   std::mem_fn(&std::thread::join));