diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 65039d20b9e9..95c15977796c 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,5 +1,11 @@
 2020-05-21  Jonathan Wakely  <jwakely@redhat.com>
 
+	PR libstdc++/93983
+	* include/bits/iterator_concepts.h (__detail::__cpp17_iterator):
+	Reorder constraints to avoid recursion when constructors use
+	iterator_traits (LWG 3420).
+	* testsuite/24_iterators/customization_points/lwg3420.cc: New test.
+
 	* include/experimental/socket (basic_socket::is_open()
 	(basic_socket_acceptor::is_open()): Use _GLIBCXX_NODISCARD macro.
 
diff --git a/libstdc++-v3/include/bits/iterator_concepts.h b/libstdc++-v3/include/bits/iterator_concepts.h
index e221ec703675..31b58408fe98 100644
--- a/libstdc++-v3/include/bits/iterator_concepts.h
+++ b/libstdc++-v3/include/bits/iterator_concepts.h
@@ -249,14 +249,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   namespace __detail
   {
+    // _GLIBCXX_RESOLVE_LIB_DEFECTS
+    // 3420. cpp17-iterator should check [type] looks like an iterator first
     template<typename _Iter>
-      concept __cpp17_iterator = copyable<_Iter>
-	&& requires(_Iter __it)
+      concept __cpp17_iterator = requires(_Iter __it)
 	{
 	  { *__it } -> __can_reference;
 	  { ++__it } -> same_as<_Iter&>;
 	  { *__it++ } -> __can_reference;
-	};
+	} && copyable<_Iter>;
 
     template<typename _Iter>
       concept __cpp17_input_iterator = __cpp17_iterator<_Iter>
@@ -269,7 +270,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 		   typename indirectly_readable_traits<_Iter>::value_type&>;
 	  typename common_reference_t<decltype(*__it++)&&,
 		   typename indirectly_readable_traits<_Iter>::value_type&>;
-	  requires signed_integral<typename incrementable_traits<_Iter>::difference_type>;
+	  requires signed_integral<
+	    typename incrementable_traits<_Iter>::difference_type>;
 	};
 
     template<typename _Iter>
diff --git a/libstdc++-v3/testsuite/24_iterators/customization_points/lwg3420.cc b/libstdc++-v3/testsuite/24_iterators/customization_points/lwg3420.cc
new file mode 100644
index 000000000000..72289a995fca
--- /dev/null
+++ b/libstdc++-v3/testsuite/24_iterators/customization_points/lwg3420.cc
@@ -0,0 +1,43 @@
+// Copyright (C) 2020 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do compile { target c++2a } }
+
+// PR libstdc++/93983
+
+// LWG 3420.
+// cpp17-iterator should check that the type looks like an iterator first
+
+#include <filesystem>
+#include <iterator>
+#include <concepts>
+
+struct Foo
+{
+  Foo(const std::filesystem::path& p);
+};
+
+static_assert(std::copyable<Foo>);
+
+struct X
+{
+  template<typename T, typename = std::iterator_traits<T>::iterator_category>
+    X(const T&);
+};
+
+static_assert(std::copyable<X>);