diff --git a/include/fmt/core.h b/include/fmt/core.h
index 8f50b533..d828a190 100644
--- a/include/fmt/core.h
+++ b/include/fmt/core.h
@@ -9,6 +9,7 @@
 #define FMT_CORE_H_
 
 #include <cassert>
+#include <cstdio>  // std::FILE
 #include <cstring>
 #include <iterator>
 #include <string>
@@ -204,6 +205,16 @@ namespace internal {
 template <typename T>
 typename std::add_rvalue_reference<T>::type declval() FMT_NOEXCEPT;
 
+template <typename>
+struct result_of;
+
+template <typename F, typename... Args>
+struct result_of<F(Args...)> {
+  // A workaround for gcc 4.4 that doesn't allow F to be a reference.
+  typedef typename std::result_of<
+    typename std::remove_reference<F>::type(Args...)>::type type;
+};
+
 // Casts nonnegative integer to unsigned.
 template <typename Int>
 FMT_CONSTEXPR typename std::make_unsigned<Int>::type to_unsigned(Int value) {
@@ -692,16 +703,6 @@ enum { max_packed_args = 15 };
 
 template <typename Context>
 class arg_map;
-
-template <typename>
-struct result_of;
-
-template <typename F, typename... Args>
-struct result_of<F(Args...)> {
-  // A workaround for gcc 4.4 that doesn't allow F to be a reference.
-  typedef typename std::result_of<
-    typename std::remove_reference<F>::type(Args...)>::type type;
-};
 }  // namespace internal
 
 // A formatting argument. It is a trivially copyable/constructible type to
@@ -1320,10 +1321,9 @@ typename std::enable_if<
   is_contiguous<Container>::value, std::back_insert_iterator<Container>>::type
     vformat_to(std::back_insert_iterator<Container> out,
                string_view format_str, format_args args) {
-  auto& container = internal::get_container(out);
-  internal::container_buffer<Container> buf(container);
+  internal::container_buffer<Container> buf(internal::get_container(out));
   vformat_to(buf, format_str, args);
-  return std::back_inserter(container);
+  return out;
 }
 
 template <typename Container>
@@ -1331,10 +1331,9 @@ typename std::enable_if<
   is_contiguous<Container>::value, std::back_insert_iterator<Container>>::type
   vformat_to(std::back_insert_iterator<Container> out,
              wstring_view format_str, wformat_args args) {
-  auto& container = internal::get_container(out);
-  internal::container_buffer<Container> buf(container);
+  internal::container_buffer<Container> buf(internal::get_container(out));
   vformat_to(buf, format_str, args);
-  return std::back_inserter(container);
+  return out;
 }
 
 std::string vformat(string_view format_str, format_args args);
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 1a8c900a..893cc4d2 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -85,13 +85,13 @@ function(add_fmt_test name)
 endfunction()
 
 add_fmt_test(assert-test)
+add_fmt_test(core-test mock-allocator.h)
 add_fmt_test(gtest-extra-test)
 add_fmt_test(format-test)
 add_fmt_test(format-impl-test)
 add_fmt_test(ostream-test)
 add_fmt_test(printf-test)
 add_fmt_test(time-test)
-add_fmt_test(util-test mock-allocator.h)
 add_fmt_test(custom-formatter-test)
 add_fmt_test(ranges-test)
 
diff --git a/test/util-test.cc b/test/core-test.cc
similarity index 100%
rename from test/util-test.cc
rename to test/core-test.cc