diff --git a/libcxx/include/deque b/libcxx/include/deque
--- a/libcxx/include/deque
+++ b/libcxx/include/deque
@@ -134,15 +134,18 @@
 template <class T, class Allocator>
     bool operator==(const deque<T,Allocator>& x, const deque<T,Allocator>& y);
 template <class T, class Allocator>
-    bool operator< (const deque<T,Allocator>& x, const deque<T,Allocator>& y);
+    bool operator< (const deque<T,Allocator>& x, const deque<T,Allocator>& y); // removed in C++20
 template <class T, class Allocator>
-    bool operator!=(const deque<T,Allocator>& x, const deque<T,Allocator>& y);
+    bool operator!=(const deque<T,Allocator>& x, const deque<T,Allocator>& y); // removed in C++20
 template <class T, class Allocator>
-    bool operator> (const deque<T,Allocator>& x, const deque<T,Allocator>& y);
+    bool operator> (const deque<T,Allocator>& x, const deque<T,Allocator>& y); // removed in C++20
 template <class T, class Allocator>
-    bool operator>=(const deque<T,Allocator>& x, const deque<T,Allocator>& y);
+    bool operator>=(const deque<T,Allocator>& x, const deque<T,Allocator>& y); // removed in C++20
 template <class T, class Allocator>
-    bool operator<=(const deque<T,Allocator>& x, const deque<T,Allocator>& y);
+    bool operator<=(const deque<T,Allocator>& x, const deque<T,Allocator>& y); // removed in C++20
+template<class T, class Allocator>
+    synth-three-way-result<T> operator<=>(const deque<T, Allocator>& x,
+                                          const deque<T, Allocator>& y);
 
 // specialized algorithms:
 template <class T, class Allocator>
@@ -165,6 +168,7 @@
 #include <__algorithm/equal.h>
 #include <__algorithm/fill_n.h>
 #include <__algorithm/lexicographical_compare.h>
+#include <__algorithm/lexicographical_compare_three_way.h>
 #include <__algorithm/min.h>
 #include <__algorithm/remove.h>
 #include <__algorithm/remove_if.h>
@@ -2342,6 +2346,8 @@
     return __sz == __y.size() && _VSTD::equal(__x.begin(), __x.end(), __y.begin());
 }
 
+#if _LIBCPP_STD_VER <= 17
+
 template <class _Tp, class _Allocator>
 inline _LIBCPP_HIDE_FROM_ABI
 bool
@@ -2382,6 +2388,19 @@
     return !(__y < __x);
 }
 
+#else // _LIBCPP_STD_VER <= 17
+
+template<class _Tp, class _Allocator>
+inline _LIBCPP_HIDE_FROM_ABI
+__synth_three_way_result<_Tp>
+operator<=>(const deque<_Tp, _Allocator>& __x, const deque<_Tp, _Allocator>& __y)
+{
+    return lexicographical_compare_three_way(
+        __x.begin(), __x.end(), __y.begin(), __y.end(), __synth_three_way);
+}
+
+#endif // _LIBCPP_STD_VER <= 17
+
 template <class _Tp, class _Allocator>
 inline _LIBCPP_HIDE_FROM_ABI
 void
diff --git a/libcxx/test/libcxx/containers/sequences/deque/compare.three_way.pass.cpp b/libcxx/test/libcxx/containers/sequences/deque/compare.three_way.pass.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/libcxx/containers/sequences/deque/compare.three_way.pass.cpp
@@ -0,0 +1,25 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+
+// <list>
+
+// template<class T, class Allocator>
+//   synth-three-way-result<T> operator<=>(const deque<T, Allocator>& x,
+//                                         const deque<T, Allocator>& y);
+
+#include <deque>
+#include <cassert>
+
+#include "test_container_comparisons.h"
+
+int main(int, char**) {
+  assert(test_ordered_container_spaceship<std::deque>());
+  // `std::deque` is not constexpr, so no `static_assert` test here.
+  return 0;
+}
\ No newline at end of file