diff --git a/llvm/include/llvm/ADT/STLExtras.h b/llvm/include/llvm/ADT/STLExtras.h
--- a/llvm/include/llvm/ADT/STLExtras.h
+++ b/llvm/include/llvm/ADT/STLExtras.h
@@ -646,13 +646,13 @@
   }
 
   template <size_t... Ns>
-  decltype(iterators) tup_inc(std::index_sequence<Ns...>) const {
-    return std::tuple<Iters...>(std::next(std::get<Ns>(iterators))...);
+  void tup_inc(std::index_sequence<Ns...>) {
+    (++std::get<Ns>(iterators), ...);
   }
 
   template <size_t... Ns>
-  decltype(iterators) tup_dec(std::index_sequence<Ns...>) const {
-    return std::tuple<Iters...>(std::prev(std::get<Ns>(iterators))...);
+  void tup_dec(std::index_sequence<Ns...>) {
+    (--std::get<Ns>(iterators), ...);
   }
 
   template <size_t... Ns>
@@ -671,14 +671,14 @@
   }
 
   ZipType &operator++() {
-    iterators = tup_inc(std::index_sequence_for<Iters...>{});
+    tup_inc(std::index_sequence_for<Iters...>{});
     return *reinterpret_cast<ZipType *>(this);
   }
 
   ZipType &operator--() {
     static_assert(Base::IsBidirectional,
                   "All inner iterators must be at least bidirectional.");
-    iterators = tup_dec(std::index_sequence_for<Iters...>{});
+    tup_dec(std::index_sequence_for<Iters...>{});
     return *reinterpret_cast<ZipType *>(this);
   }
 
@@ -769,10 +769,9 @@
 
 namespace detail {
 template <typename Iter>
-Iter next_or_end(const Iter &I, const Iter &End) {
-  if (I == End)
-    return End;
-  return std::next(I);
+void increment_if_not_end(Iter &I, const Iter &End) {
+  if (I != End)
+    ++I;
 }
 
 template <typename Iter>
@@ -826,9 +825,8 @@
   }
 
   template <size_t... Ns>
-  decltype(iterators) tup_inc(std::index_sequence<Ns...>) const {
-    return std::tuple<Iters...>(
-        next_or_end(std::get<Ns>(iterators), std::get<Ns>(end_iterators))...);
+  void tup_inc(std::index_sequence<Ns...>) {
+    (increment_if_not_end(std::get<Ns>(iterators), std::get<Ns>(end_iterators)), ...);
   }
 
 public:
@@ -841,7 +839,7 @@
   }
 
   zip_longest_iterator<Iters...> &operator++() {
-    iterators = tup_inc(std::index_sequence_for<Iters...>{});
+    tup_inc(std::index_sequence_for<Iters...>{});
     return *this;
   }
 
diff --git a/llvm/unittests/ADT/STLExtrasTest.cpp b/llvm/unittests/ADT/STLExtrasTest.cpp
--- a/llvm/unittests/ADT/STLExtrasTest.cpp
+++ b/llvm/unittests/ADT/STLExtrasTest.cpp
@@ -881,6 +881,57 @@
   EXPECT_EQ(2, Destructors);
 }
 
+
+TEST(STLExtrasTest, Zip) {
+  struct CountingIterator {
+    // For std::iterator_traits
+    using difference_type = int;
+    using value_type = int;
+    using pointer = void;
+    using reference = int;
+    using iterator_category = std::input_iterator_tag;
+
+    // Test that zip does not require copy assign operator
+    CountingIterator& operator=(const CountingIterator& other) = delete;
+
+    CountingIterator(int count) : count(count) {}
+    CountingIterator(const CountingIterator& other) : count(other.count) {}
+    bool operator==(const CountingIterator& other) const { return count == other.count; }
+    bool operator!=(const CountingIterator& other) const { return !(*this == other); }
+    CountingIterator& operator++() { ++count; return *this; }
+    int operator*() const { return count; }
+    int count;
+  };
+
+  auto r1 = make_range(CountingIterator(5), CountingIterator(9));
+  auto r2 = make_range(CountingIterator(8), CountingIterator(11));
+
+  {
+    auto zip_range = zip(r1, r2);
+    auto it = zip_range.begin();
+    EXPECT_EQ(*it, std::make_tuple(5, 8));
+    ++it;
+    EXPECT_EQ(*it, std::make_tuple(6, 9));
+    ++it;
+    EXPECT_EQ(*it, std::make_tuple(7, 10));
+    ++it;
+    EXPECT_EQ(it, zip_range.end());
+  }
+  {
+    auto zip_range = zip_longest(r1, r2);
+    auto it = zip_range.begin();
+    EXPECT_EQ(*it, std::make_tuple(5, 8));
+    ++it;
+    EXPECT_EQ(*it, std::make_tuple(6, 9));
+    ++it;
+    EXPECT_EQ(*it, std::make_tuple(7, 10));
+    ++it;
+    EXPECT_EQ(*it, std::make_tuple(8, None));
+    ++it;
+    EXPECT_EQ(it, zip_range.end());
+  }
+}
+
 TEST(STLExtrasTest, AllOfZip) {
   std::vector<int> v1 = {0, 4, 2, 1};
   std::vector<int> v2 = {1, 4, 3, 6};