Index: include/llvm/ADT/ilist_iterator.h
===================================================================
--- include/llvm/ADT/ilist_iterator.h
+++ include/llvm/ADT/ilist_iterator.h
@@ -86,10 +86,10 @@
   ilist_iterator() : NodePtr(nullptr) {}
 
   // This is templated so that we can allow constructing a const iterator from
-  // a nonconst iterator...
-  template <bool RHSIsConst>
+  // a nonconst iterator and switch between reverse/forward iterators...
+  template <bool RHSIsConst, bool RHSIsReverse>
   ilist_iterator(
-      const ilist_iterator<OptionsT, IsReverse, RHSIsConst> &RHS,
+      const ilist_iterator<OptionsT, RHSIsReverse, RHSIsConst> &RHS,
       typename std::enable_if<IsConst || !RHSIsConst, void *>::type = nullptr)
       : NodePtr(RHS.NodePtr) {}
 
Index: unittests/ADT/SimpleIListTest.cpp
===================================================================
--- unittests/ADT/SimpleIListTest.cpp
+++ unittests/ADT/SimpleIListTest.cpp
@@ -193,6 +193,20 @@
   EXPECT_EQ(A.getReverseIterator(), ReverseIter);
   ++ReverseIter;
   EXPECT_EQ(L.rend(), ReverseIter);
+
+  // Check conversion between reverse/forward iterators.
+  typedef simple_ilist<Node>::reverse_iterator reverse_iterator;
+  typedef simple_ilist<Node>::iterator iterator;
+  EXPECT_EQ(reverse_iterator(L.begin()), std::prev(L.rend()));
+  EXPECT_EQ(reverse_iterator(std::prev(L.end())), L.rbegin());
+  EXPECT_EQ(iterator(L.rbegin()), std::prev(L.end()));
+  EXPECT_EQ(iterator(std::prev(L.rend())), L.begin());
+  for (Node &N : L) {
+    EXPECT_EQ(iterator(reverse_iterator(N.getIterator())),
+              N.getIterator());
+    EXPECT_EQ(reverse_iterator(iterator(N.getReverseIterator())),
+              N.getReverseIterator());
+  }
 }
 
 TEST(SimpleIListTest, eraseAndDispose) {