Index: include/memory
===================================================================
--- include/memory
+++ include/memory
@@ -3924,7 +3924,10 @@
 
     template <class _Yp, class _OrigPtr>
         _LIBCPP_INLINE_VISIBILITY
-        void
+        typename enable_if<is_convertible<_OrigPtr*,
+                                          const enable_shared_from_this<_Yp>*
+        >::value,
+            void>::type
         __enable_weak_this(const enable_shared_from_this<_Yp>* __e,
                            _OrigPtr* __ptr) _NOEXCEPT
         {
@@ -3943,6 +3946,7 @@
     template <class _Up> friend class _LIBCPP_TEMPLATE_VIS weak_ptr;
 };
 
+
 template<class _Tp>
 inline
 _LIBCPP_CONSTEXPR
Index: test/std/utilities/memory/util.smartptr/util.smartptr.enab/enable_shared_from_this.pass.cpp
===================================================================
--- test/std/utilities/memory/util.smartptr/util.smartptr.enab/enable_shared_from_this.pass.cpp
+++ test/std/utilities/memory/util.smartptr/util.smartptr.enab/enable_shared_from_this.pass.cpp
@@ -49,6 +49,11 @@
 };
 
 
+struct PrivateBase : private std::enable_shared_from_this<PrivateBase> {
+    std::weak_ptr<PrivateBase> get_weak() { return weak_from_this(); }
+};
+
+
 int main()
 {
     {  // https://bugs.llvm.org/show_bug.cgi?id=18843
@@ -74,6 +79,12 @@
     assert(p == q);
     assert(!p.owner_before(q) && !q.owner_before(p)); // p and q share ownership
     }
+  {
+    typedef std::shared_ptr<PrivateBase> APtr;
+    typedef std::weak_ptr<PrivateBase> WeakAPtr;
+    APtr a1 = std::make_shared<PrivateBase>();
+    assert(a1.use_count() == 1);
+  }
     // Test LWG issue 2529. Only reset '__weak_ptr_' when it's already expired.
     // http://cplusplus.github.io/LWG/lwg-active.html#2529.
     // Test two different ways: