diff --git a/libcxx/include/__functional/hash.h b/libcxx/include/__functional/hash.h
--- a/libcxx/include/__functional/hash.h
+++ b/libcxx/include/__functional/hash.h
@@ -75,10 +75,10 @@
     switch (__len)
     {
     case 3:
-        __h ^= __data[2] << 16;
+        __h ^= static_cast<_Size>(__data[2] << 16);
         _LIBCPP_FALLTHROUGH();
     case 2:
-        __h ^= __data[1] << 8;
+        __h ^= static_cast<_Size>(__data[1] << 8);
         _LIBCPP_FALLTHROUGH();
     case 1:
         __h ^= __data[0];
@@ -140,9 +140,9 @@
       return __hash_len_16(__len + (__a << 3), __b);
     }
     if (__len > 0) {
-      const unsigned char __a = __s[0];
-      const unsigned char __b = __s[__len >> 1];
-      const unsigned char __c = __s[__len - 1];
+      const unsigned char __a = static_cast<unsigned char>(__s[0]);
+      const unsigned char __b = static_cast<unsigned char>(__s[__len >> 1]);
+      const unsigned char __c = static_cast<unsigned char>(__s[__len - 1]);
       const uint32_t __y = static_cast<uint32_t>(__a) +
                            (static_cast<uint32_t>(__b) << 8);
       const uint32_t __z = __len + (static_cast<uint32_t>(__c) << 2);
diff --git a/libcxx/include/__iterator/advance.h b/libcxx/include/__iterator/advance.h
--- a/libcxx/include/__iterator/advance.h
+++ b/libcxx/include/__iterator/advance.h
@@ -32,15 +32,15 @@
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _InputIter>
-inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 void
-__advance(_InputIter& __i, typename iterator_traits<_InputIter>::difference_type __n, input_iterator_tag) {
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX14
+void __advance(_InputIter& __i, typename iterator_traits<_InputIter>::difference_type __n, input_iterator_tag) {
   for (; __n > 0; --__n)
     ++__i;
 }
 
 template <class _BiDirIter>
-inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 void
-__advance(_BiDirIter& __i, typename iterator_traits<_BiDirIter>::difference_type __n, bidirectional_iterator_tag) {
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX14
+void __advance(_BiDirIter& __i, typename iterator_traits<_BiDirIter>::difference_type __n, bidirectional_iterator_tag) {
   if (__n >= 0)
     for (; __n > 0; --__n)
       ++__i;
@@ -50,17 +50,19 @@
 }
 
 template <class _RandIter>
-inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 void
-__advance(_RandIter& __i, typename iterator_traits<_RandIter>::difference_type __n, random_access_iterator_tag) {
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX14
+void __advance(_RandIter& __i, typename iterator_traits<_RandIter>::difference_type __n, random_access_iterator_tag) {
   __i += __n;
 }
 
 template <
     class _InputIter, class _Distance,
-    class = typename enable_if<is_integral<decltype(_VSTD::__convert_to_integral(declval<_Distance>()))>::value>::type>
-inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14 void advance(_InputIter& __i, _Distance __orig_n) {
-  typedef decltype(_VSTD::__convert_to_integral(__orig_n)) _IntegralSize;
-  _IntegralSize __n = __orig_n;
+    class _IntegralDistance = decltype(_VSTD::__convert_to_integral(declval<_Distance>())),
+    class = _EnableIf<is_integral<_IntegralDistance>::value> >
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX14
+void advance(_InputIter& __i, _Distance __orig_n) {
+  typedef typename iterator_traits<_InputIter>::difference_type _Difference;
+  _Difference __n = static_cast<_Difference>(_VSTD::__convert_to_integral(__orig_n));
   _LIBCPP_ASSERT(__n >= 0 || __is_cpp17_bidirectional_iterator<_InputIter>::value,
                  "Attempt to advance(it, n) with negative n on a non-bidirectional iterator");
   _VSTD::__advance(__i, __n, typename iterator_traits<_InputIter>::iterator_category());
diff --git a/libcxx/include/tuple b/libcxx/include/tuple
--- a/libcxx/include/tuple
+++ b/libcxx/include/tuple
@@ -1165,7 +1165,7 @@
 
 namespace __find_detail {
 
-static constexpr size_t __not_found = -1;
+static constexpr size_t __not_found = static_cast<size_t>(-1);
 static constexpr size_t __ambiguous = __not_found - 1;
 
 inline _LIBCPP_INLINE_VISIBILITY
diff --git a/libcxx/test/std/iterators/iterator.primitives/iterator.operations/advance.pass.cpp b/libcxx/test/std/iterators/iterator.primitives/iterator.operations/advance.pass.cpp
--- a/libcxx/test/std/iterators/iterator.primitives/iterator.operations/advance.pass.cpp
+++ b/libcxx/test/std/iterators/iterator.primitives/iterator.operations/advance.pass.cpp
@@ -20,7 +20,7 @@
 //   constexpr void advance(Iter& i, Distance n);
 
 // Make sure we catch forced conversions to the difference_type if they happen.
-// ADDITIONAL_COMPILER_FLAGS: -Wsign-conversion
+// ADDITIONAL_COMPILE_FLAGS: -Wsign-conversion
 
 #include <iterator>
 #include <cassert>
@@ -42,21 +42,37 @@
 TEST_CONSTEXPR_CXX17 bool tests()
 {
     const char* s = "1234567890";
-    typedef std::iterator_traits<const char*>::difference_type Distance;
-    check_advance<Distance>(cpp17_input_iterator<const char*>(s), 10, cpp17_input_iterator<const char*>(s+10));
-    check_advance<Distance>(forward_iterator<const char*>(s), 10, forward_iterator<const char*>(s+10));
-    check_advance<Distance>(bidirectional_iterator<const char*>(s+5), 5, bidirectional_iterator<const char*>(s+10));
-    check_advance<Distance>(bidirectional_iterator<const char*>(s+5), -5, bidirectional_iterator<const char*>(s));
-    check_advance<Distance>(random_access_iterator<const char*>(s+5), 5, random_access_iterator<const char*>(s+10));
-    check_advance<Distance>(random_access_iterator<const char*>(s+5), -5, random_access_iterator<const char*>(s));
-    check_advance<Distance>(s+5, 5, s+10);
-    check_advance<Distance>(s+5, -5, s);
+
+    // Check with iterator_traits::difference_type
+    {
+        typedef std::iterator_traits<const char*>::difference_type Distance;
+        check_advance<Distance>(cpp17_input_iterator<const char*>(s), 10, cpp17_input_iterator<const char*>(s+10));
+        check_advance<Distance>(forward_iterator<const char*>(s), 10, forward_iterator<const char*>(s+10));
+        check_advance<Distance>(bidirectional_iterator<const char*>(s+5), 5, bidirectional_iterator<const char*>(s+10));
+        check_advance<Distance>(bidirectional_iterator<const char*>(s+5), -5, bidirectional_iterator<const char*>(s));
+        check_advance<Distance>(random_access_iterator<const char*>(s+5), 5, random_access_iterator<const char*>(s+10));
+        check_advance<Distance>(random_access_iterator<const char*>(s+5), -5, random_access_iterator<const char*>(s));
+        check_advance<Distance>(s+5, 5, s+10);
+        check_advance<Distance>(s+5, -5, s);
+    }
 
     // Also check with other distance types
-    check_advance<std::size_t>(cpp17_input_iterator<const char*>(s), 10u, cpp17_input_iterator<const char*>(s+10));
-    check_advance<std::size_t>(forward_iterator<const char*>(s), 10u, forward_iterator<const char*>(s+10));
-    check_advance<std::size_t>(bidirectional_iterator<const char*>(s), 10u, bidirectional_iterator<const char*>(s+10));
-    check_advance<std::size_t>(random_access_iterator<const char*>(s), 10u, random_access_iterator<const char*>(s+10));
+    {
+        typedef int Distance;
+        check_advance<Distance>(cpp17_input_iterator<const char*>(s), 10, cpp17_input_iterator<const char*>(s+10));
+        check_advance<Distance>(forward_iterator<const char*>(s), 10, forward_iterator<const char*>(s+10));
+        check_advance<Distance>(bidirectional_iterator<const char*>(s), 10, bidirectional_iterator<const char*>(s+10));
+        check_advance<Distance>(random_access_iterator<const char*>(s), 10, random_access_iterator<const char*>(s+10));
+    }
+
+    // Check with unsigned distance types to catch signedness-change issues
+    {
+        typedef std::size_t Distance;
+        check_advance<Distance>(cpp17_input_iterator<const char*>(s), 10u, cpp17_input_iterator<const char*>(s+10));
+        check_advance<Distance>(forward_iterator<const char*>(s), 10u, forward_iterator<const char*>(s+10));
+        check_advance<Distance>(bidirectional_iterator<const char*>(s), 10u, bidirectional_iterator<const char*>(s+10));
+        check_advance<Distance>(random_access_iterator<const char*>(s), 10u, random_access_iterator<const char*>(s+10));
+    }
 
     return true;
 }