diff --git a/include/fmt/core.h b/include/fmt/core.h
index b4c511fe..2e9e8451 100644
--- a/include/fmt/core.h
+++ b/include/fmt/core.h
@@ -1202,7 +1202,27 @@ FMT_CONSTEXPR_DECL FMT_INLINE auto visit_format_arg(
   return vis(monostate());
 }
 
+// Checks whether T is a container with contiguous storage.
+template <typename T> struct is_contiguous : std::false_type {};
+template <typename Char>
+struct is_contiguous<std::basic_string<Char>> : std::true_type {};
+template <typename Char>
+struct is_contiguous<detail::buffer<Char>> : std::true_type {};
+
 namespace detail {
+
+template <typename OutputIt>
+struct is_back_insert_iterator : std::false_type {};
+template <typename Container>
+struct is_back_insert_iterator<std::back_insert_iterator<Container>>
+    : std::true_type {};
+
+template <typename OutputIt>
+struct is_contiguous_back_insert_iterator : std::false_type {};
+template <typename Container>
+struct is_contiguous_back_insert_iterator<std::back_insert_iterator<Container>>
+    : is_contiguous<Container> {};
+
 // A type-erased reference to an std::locale to avoid heavy <locale> include.
 class locale_ref {
  private:
@@ -1329,7 +1349,9 @@ template <typename OutputIt, typename Char> class basic_format_context {
   iterator out() { return out_; }
 
   // Advances the begin iterator to ``it``.
-  void advance_to(iterator it) { out_ = it; }
+  void advance_to(iterator it) {
+    if (!detail::is_back_insert_iterator<iterator>()) out_ = it;
+  }
 
   detail::locale_ref locale() { return loc_; }
 };
@@ -1715,22 +1737,8 @@ struct wformat_args : basic_format_args<wformat_context> {
   using basic_format_args::basic_format_args;
 };
 
-template <typename Container> struct is_contiguous : std::false_type {};
-
-template <typename Char>
-struct is_contiguous<std::basic_string<Char>> : std::true_type {};
-
-template <typename Char>
-struct is_contiguous<detail::buffer<Char>> : std::true_type {};
-
 namespace detail {
 
-template <typename OutputIt>
-struct is_contiguous_back_insert_iterator : std::false_type {};
-template <typename Container>
-struct is_contiguous_back_insert_iterator<std::back_insert_iterator<Container>>
-    : is_contiguous<Container> {};
-
 // Reports a compile-time error if S is not a valid format string.
 template <typename..., typename S, FMT_ENABLE_IF(!is_compile_string<S>::value)>
 FMT_INLINE void check_format_string(const S&) {