diff --git a/benchmarks/CMakeLists.txt b/benchmarks/CMakeLists.txt
index 253fbd684..a4105be08 100644
--- a/benchmarks/CMakeLists.txt
+++ b/benchmarks/CMakeLists.txt
@@ -69,6 +69,7 @@ set(BENCHMARK_NATIVE_INSTALL ${CMAKE_CURRENT_BINARY_DIR}/benchmark-native)
 set(BENCHMARK_TEST_COMPILE_FLAGS
     -std=c++14 -O2
     -I${BENCHMARK_LIBCXX_INSTALL}/include
+    -I${LIBCXX_SOURCE_DIR}/test/support
 )
 set(BENCHMARK_TEST_LIBCXX_COMPILE_FLAGS
     -nostdinc++
diff --git a/benchmarks/filesystem.bench.cpp b/benchmarks/filesystem.bench.cpp
index 2cea3f69c..f7949a163 100644
--- a/benchmarks/filesystem.bench.cpp
+++ b/benchmarks/filesystem.bench.cpp
@@ -2,6 +2,7 @@
 
 #include "benchmark/benchmark_api.h"
 #include "GenerateInput.hpp"
+#include "test_iterators.h"
 
 namespace fs = std::experimental::filesystem;
 
@@ -41,6 +42,39 @@ void BM_PathConstructCStr(benchmark::State &st, GenInputs gen) {
 BENCHMARK_CAPTURE(BM_PathConstructCStr, large_string,
   getRandomStringInputs)->Arg(TestNumInputs);
 
+
+template <template <class...> class ItType, class GenInputs>
+void BM_PathConstructIter(benchmark::State &st, GenInputs gen) {
+  using namespace fs;
+  using Iter = ItType<std::string::const_iterator>;
+  const auto in = gen(st.range(0));
+  path PP;
+  for (auto& Part : in)
+    PP /= Part;
+  auto Start = Iter(PP.native().begin());
+  auto End = Iter(PP.native().end());
+  benchmark::DoNotOptimize(PP.native().data());
+  benchmark::DoNotOptimize(Start);
+  benchmark::DoNotOptimize(End);
+  while (st.KeepRunning()) {
+    const path P(Start, End);
+    benchmark::DoNotOptimize(P.native().data());
+  }
+}
+template <class GenInputs>
+void BM_PathConstructInputIter(benchmark::State &st, GenInputs gen) {
+  BM_PathConstructIter<input_iterator>(st, gen);
+}
+template <class GenInputs>
+void BM_PathConstructForwardIter(benchmark::State &st, GenInputs gen) {
+  BM_PathConstructIter<forward_iterator>(st, gen);
+}
+BENCHMARK_CAPTURE(BM_PathConstructInputIter, large_string,
+  getRandomStringInputs)->Arg(TestNumInputs);
+BENCHMARK_CAPTURE(BM_PathConstructForwardIter, large_string,
+  getRandomStringInputs)->Arg(TestNumInputs);
+
+
 template <class GenInputs>
 void BM_PathIterateMultipleTimes(benchmark::State &st, GenInputs gen) {
   using namespace fs;
diff --git a/include/experimental/filesystem b/include/experimental/filesystem
index c674a0369..410235f11 100644
--- a/include/experimental/filesystem
+++ b/include/experimental/filesystem
@@ -625,8 +625,18 @@ template <>
 struct _PathCVT<char> {
 
     template <class _Iter>
-    static void __append_range(string& __dest, _Iter __b, _Iter __e) {
-        __dest.append(__b, __e);
+    static typename enable_if<
+        __is_exactly_input_iterator<_Iter>::value
+    >::type __append_range(string& __dest, _Iter __b, _Iter __e) {
+        for (; __b != __e; ++__b)
+            __dest.push_back(*__b);
+    }
+
+    template <class _Iter>
+    static typename enable_if<
+        __is_forward_iterator<_Iter>::value
+    >::type __append_range(string& __dest, _Iter __b, _Iter __e) {
+        __dest.__append_forward_unsafe(__b, __e);
     }
 
     template <class _Iter>
diff --git a/include/string b/include/string
index b56ab384b..95fbce041 100644
--- a/include/string
+++ b/include/string
@@ -926,6 +926,8 @@ public:
     basic_string& append(const value_type* __s, size_type __n);
     basic_string& append(const value_type* __s);
     basic_string& append(size_type __n, value_type __c);
+    template <class _ForwardIterator>
+    basic_string& __append_forward_unsafe(_ForwardIterator, _ForwardIterator);
     template<class _InputIterator>
         typename enable_if
         <
@@ -933,7 +935,12 @@ public:
                 || !__libcpp_string_gets_noexcept_iterator<_InputIterator>::value,
             basic_string&
         >::type
-        append(_InputIterator __first, _InputIterator __last);
+    _LIBCPP_INLINE_VISIBILITY
+    append(_InputIterator __first, _InputIterator __last) {
+      const basic_string __temp (__first, __last, __alloc());
+      append(__temp.data(), __temp.size());
+      return *this;
+    }
     template<class _ForwardIterator>
         typename enable_if
         <
@@ -941,7 +948,11 @@ public:
                 && __libcpp_string_gets_noexcept_iterator<_ForwardIterator>::value,
             basic_string&
         >::type
-        append(_ForwardIterator __first, _ForwardIterator __last);
+    _LIBCPP_INLINE_VISIBILITY
+    append(_ForwardIterator __first, _ForwardIterator __last) {
+      return __append_forward_unsafe(__first, __last);
+    }
+
 #ifndef _LIBCPP_HAS_NO_GENERALIZED_INITIALIZERS
     _LIBCPP_INLINE_VISIBILITY
     basic_string& append(initializer_list<value_type> __il) {return append(__il.begin(), __il.size());}
@@ -2182,21 +2193,6 @@ basic_string<_CharT, _Traits, _Allocator>::push_back(value_type __c)
     traits_type::assign(*++__p, value_type());
 }
 
-template <class _CharT, class _Traits, class _Allocator>
-template<class _InputIterator>
-typename enable_if
-<
-    __is_exactly_input_iterator<_InputIterator>::value
-             || !__libcpp_string_gets_noexcept_iterator<_InputIterator>::value,
-    basic_string<_CharT, _Traits, _Allocator>&
->::type
-basic_string<_CharT, _Traits, _Allocator>::append(_InputIterator __first, _InputIterator __last)
-{
-    const basic_string __temp (__first, __last, __alloc());
-    append(__temp.data(), __temp.size());
-    return *this;
-}
-
 template <class _Tp>
 bool __ptr_in_range (const _Tp* __p, const _Tp* __first, const _Tp* __last)
 {
@@ -2211,14 +2207,12 @@ bool __ptr_in_range (const _Tp1* __p, const _Tp2* __first, const _Tp2* __last)
 
 template <class _CharT, class _Traits, class _Allocator>
 template<class _ForwardIterator>
-typename enable_if
-<
-    __is_forward_iterator<_ForwardIterator>::value
-          && __libcpp_string_gets_noexcept_iterator<_ForwardIterator>::value,
-    basic_string<_CharT, _Traits, _Allocator>&
->::type
-basic_string<_CharT, _Traits, _Allocator>::append(_ForwardIterator __first, _ForwardIterator __last)
+basic_string<_CharT, _Traits, _Allocator>&
+basic_string<_CharT, _Traits, _Allocator>::__append_forward_unsafe(
+    _ForwardIterator __first, _ForwardIterator __last)
 {
+    static_assert(__is_forward_iterator<_ForwardIterator>::value,
+                  "function requires a ForwardIterator");
     size_type __sz = size();
     size_type __cap = capacity();
     size_type __n = static_cast<size_type>(_VSTD::distance(__first, __last));