diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index a77596e784e..267ec3999f2 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,3 +1,16 @@
+2018-11-22  Jonathan Wakely  <jwakely@redhat.com>
+
+	PR libstdc++/85930
+	PR libstdc++/87520
+	* include/bits/shared_ptr_base.h (_Sp_make_shared_tag::_S_ti)
+	[__cpp_rtti]: Define even when RTTI is enabled. Use array of
+	sizeof(type_info) so that type-punned reference binds to an object
+	of the correct size as well as correct alignment.
+	(_Sp_counted_ptr_inplace::_M_get_deleter) [__cpp_rtti]: Check for
+	_S_ti() reference even when RTTI is enabled.
+	(__shared_ptr(_Sp_make_shared_tag, const _Alloc&, _Args&&...))
+	[__cpp_rtti]: Pass _S_ti() instead of typeid(_Sp_make_shared_tag).
+
 2018-11-21  Jakub Jelinek  <jakub@redhat.com>
 
 	PR c++/87386
diff --git a/libstdc++-v3/include/bits/shared_ptr_base.h b/libstdc++-v3/include/bits/shared_ptr_base.h
index 870aeb9bfda..46ff4a7cf29 100644
--- a/libstdc++-v3/include/bits/shared_ptr_base.h
+++ b/libstdc++-v3/include/bits/shared_ptr_base.h
@@ -500,7 +500,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   struct _Sp_make_shared_tag
   {
-#if !__cpp_rtti
   private:
     template<typename _Tp, _Lock_policy _Lp>
       friend class __shared_ptr;
@@ -510,10 +509,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     static const type_info&
     _S_ti() noexcept _GLIBCXX_VISIBILITY(default)
     {
-      alignas(type_info) static constexpr _Sp_make_shared_tag __tag;
+      alignas(type_info) static constexpr char __tag[sizeof(type_info)] = { };
       return reinterpret_cast<const type_info&>(__tag);
     }
-#endif
   };
 
   template<typename _Tp, typename _Alloc, _Lock_policy _Lp>
@@ -562,16 +560,20 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	this->~_Sp_counted_ptr_inplace();
       }
 
-      // Sneaky trick so __shared_ptr can get the managed pointer
+      // Sneaky trick so __shared_ptr can get the managed pointer.
       virtual void*
-      _M_get_deleter(const std::type_info& __ti) noexcept
+      _M_get_deleter(const std::type_info& __ti) noexcept override
       {
-#if __cpp_rtti
-	if (__ti == typeid(_Sp_make_shared_tag))
-#else
+	// Check for the fake type_info first, so we don't try to access it
+	// as a real type_info object.
 	if (&__ti == &_Sp_make_shared_tag::_S_ti())
-#endif
 	  return const_cast<typename remove_cv<_Tp>::type*>(_M_ptr());
+#if __cpp_rtti
+	// Callers compiled with old libstdc++ headers and RTTI enabled
+	// might pass this instead:
+	else if (__ti == typeid(_Sp_make_shared_tag))
+	  return const_cast<typename remove_cv<_Tp>::type*>(_M_ptr());
+#endif
 	return nullptr;
       }
 
@@ -1323,11 +1325,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	{
 	  // _M_ptr needs to point to the newly constructed object.
 	  // This relies on _Sp_counted_ptr_inplace::_M_get_deleter.
-#if __cpp_rtti
-	  void* __p = _M_refcount._M_get_deleter(typeid(__tag));
-#else
 	  void* __p = _M_refcount._M_get_deleter(_Sp_make_shared_tag::_S_ti());
-#endif
 	  _M_ptr = static_cast<_Tp*>(__p);
 	  _M_enable_shared_from_this_with(_M_ptr);
 	}