diff --git a/libcxx/include/algorithm b/libcxx/include/algorithm
index 244ae2d..326e566 100644
--- a/libcxx/include/algorithm
+++ b/libcxx/include/algorithm
@@ -785,6 +785,7 @@
     __debug_less(_Compare& __c) : __comp_(__c) {}
 
     template <class _Tp, class _Up>
+    _LIBCPP_CONSTEXPR_AFTER_CXX17
     bool operator()(const _Tp& __x,  const _Up& __y)
     {
         bool __r = __comp_(__x, __y);
diff --git a/libcxx/test/libcxx/algorithms/debug_less.pass.cpp b/libcxx/test/libcxx/algorithms/debug_less.pass.cpp
index 260900b..5d1b575 100644
--- a/libcxx/test/libcxx/algorithms/debug_less.pass.cpp
+++ b/libcxx/test/libcxx/algorithms/debug_less.pass.cpp
@@ -268,6 +268,16 @@
     assert(dl(static_cast<int&&>(1), static_cast<const int&&>(2)));
 }
 
+#if TEST_STD_VER > 17
+constexpr bool test_constexpr() {
+    std::less<> cmp{};
+    __debug_less<std::less<> > dcmp(cmp);
+    assert(dcmp(1, 2));
+    assert(!dcmp(1, 1));
+    return true;
+}
+#endif
+
 int main(int, char**) {
     test_passing();
     test_failing();
@@ -275,5 +285,8 @@
     test_non_const_arg_cmp();
     test_value_iterator();
     test_value_categories();
+#if TEST_STD_VER > 17
+    static_assert(test_constexpr(), "");
+#endif
     return 0;
 }