diff --git a/stl/inc/flat_map b/stl/inc/flat_map
index 1e6eac4961b..d50232d3b1e 100644
--- a/stl/inc/flat_map
+++ b/stl/inc/flat_map
@@ -1099,25 +1099,14 @@ private:
         return _Count;
     }
 
-    template <class _KeyTy>
-    _NODISCARD iterator _Find(const _KeyTy& _Key_val) {
+    template <class _SelfTy, class _KeyTy>
+    _NODISCARD auto _Find(this _SelfTy& _Self, const _KeyTy& _Key_val) {
         _STL_INTERNAL_STATIC_ASSERT(is_same_v<_KeyTy, key_type> || _Transparent<key_compare>);
-        iterator _Position = lower_bound(_Key_val);
-        if (_Position != end() && !_Key_compare(_Key_val, _Position->first)) {
+        const auto _Position = _Self.lower_bound(_Key_val);
+        if (_Position != _Self.end() && !_Self._Key_compare(_Key_val, _Position->first)) {
             return _Position;
         } else {
-            return end();
-        }
-    }
-
-    template <class _KeyTy>
-    _NODISCARD const_iterator _Find(const _KeyTy& _Key_val) const {
-        _STL_INTERNAL_STATIC_ASSERT(is_same_v<_KeyTy, key_type> || _Transparent<key_compare>);
-        const_iterator _Position = lower_bound(_Key_val);
-        if (_Position != cend() && !_Key_compare(_Key_val, _Position->first)) {
-            return _Position;
-        } else {
-            return cend();
+            return _Self.end();
         }
     }
 
@@ -1133,74 +1122,37 @@ private:
         return find(_Key_val) != cend();
     }
 
-    template <class _KeyTy>
-    _NODISCARD iterator _Lower_bound(const _KeyTy& _Key_val) {
+    template <class _SelfTy, class _KeyTy, class _BoundFn>
+    _NODISCARD auto _Find_bound(this _SelfTy& _Self, const _KeyTy& _Key_val, _BoundFn _Bound_fun) {
         _STL_INTERNAL_STATIC_ASSERT(is_same_v<_KeyTy, key_type> || _Transparent<key_compare>);
-        const auto _Key_unchecked_begin = _STD _Get_unwrapped(_STD cbegin(_Data.keys));
-        const auto _Key_unchecked_it    = _STD lower_bound(
-               _Key_unchecked_begin, _STD _Get_unwrapped(_STD cend(_Data.keys)), _Key_val, _Pass_key_comp());
+        const auto _Key_unchecked_begin = _STD _Get_unwrapped(_STD cbegin(_Self._Data.keys));
+        const auto _Key_unchecked_it    = _Bound_fun(
+            _Key_unchecked_begin, _STD _Get_unwrapped(_STD cend(_Self._Data.keys)), _Key_val, _Self._Pass_key_comp());
         const auto _Dist = _Key_unchecked_it - _Key_unchecked_begin;
 
-        auto _Key_it = _STD cbegin(_Data.keys);
-        _STD _Seek_wrapped(_Key_it, _Key_unchecked_it);
-        auto _Val_it = _Data.values.begin() + static_cast<_RANGES range_difference_t<_MappedContainer>>(_Dist);
-        return iterator{_STD move(_Key_it), _STD move(_Val_it)};
-    }
-
-    template <class _KeyTy>
-    _NODISCARD const_iterator _Lower_bound(const _KeyTy& _Key_val) const {
-        _STL_INTERNAL_STATIC_ASSERT(is_same_v<_KeyTy, key_type> || _Transparent<key_compare>);
-        const auto _Key_unchecked_begin = _STD _Get_unwrapped(_STD cbegin(_Data.keys));
-        const auto _Key_unchecked_it    = _STD lower_bound(
-               _Key_unchecked_begin, _STD _Get_unwrapped(_STD cend(_Data.keys)), _Key_val, _Pass_key_comp());
-        const auto _Dist = _Key_unchecked_it - _Key_unchecked_begin;
-
-        auto _Key_it = _STD cbegin(_Data.keys);
+        auto _Key_it = _STD cbegin(_Self._Data.keys);
         _STD _Seek_wrapped(_Key_it, _Key_unchecked_it);
         auto _Val_it =
-            _STD cbegin(_Data.values) + static_cast<_RANGES range_difference_t<const _MappedContainer>>(_Dist);
-        return const_iterator{_STD move(_Key_it), _STD move(_Val_it)};
-    }
-
-    template <class _KeyTy>
-    _NODISCARD iterator _Upper_bound(const _KeyTy& _Key_val) {
-        _STL_INTERNAL_STATIC_ASSERT(is_same_v<_KeyTy, key_type> || _Transparent<key_compare>);
-        const auto _Key_unchecked_begin = _STD _Get_unwrapped(_STD cbegin(_Data.keys));
-        const auto _Key_unchecked_it    = _STD upper_bound(
-               _Key_unchecked_begin, _STD _Get_unwrapped(_STD cend(_Data.keys)), _Key_val, _Pass_key_comp());
-        const auto _Dist = _Key_unchecked_it - _Key_unchecked_begin;
+            _STD begin(_Self._Data.values) + static_cast<_RANGES range_difference_t<mapped_container_type>>(_Dist);
 
-        auto _Key_it = _STD cbegin(_Data.keys);
-        _STD _Seek_wrapped(_Key_it, _Key_unchecked_it);
-        auto _Val_it = _Data.values.begin() + static_cast<_RANGES range_difference_t<_MappedContainer>>(_Dist);
-        return iterator{_STD move(_Key_it), _STD move(_Val_it)};
+        using _Maybe_const_iter = conditional_t<is_const_v<_SelfTy>, const_iterator, iterator>;
+        return _Maybe_const_iter{_STD move(_Key_it), _STD move(_Val_it)};
     }
 
-    template <class _KeyTy>
-    _NODISCARD const_iterator _Upper_bound(const _KeyTy& _Key_val) const {
-        _STL_INTERNAL_STATIC_ASSERT(is_same_v<_KeyTy, key_type> || _Transparent<key_compare>);
-        const auto _Key_unchecked_begin = _STD _Get_unwrapped(_STD cbegin(_Data.keys));
-        const auto _Key_unchecked_it    = _STD upper_bound(
-               _Key_unchecked_begin, _STD _Get_unwrapped(_STD cend(_Data.keys)), _Key_val, _Pass_key_comp());
-        const auto _Dist = _Key_unchecked_it - _Key_unchecked_begin;
-
-        auto _Key_it = _STD cbegin(_Data.keys);
-        _STD _Seek_wrapped(_Key_it, _Key_unchecked_it);
-        auto _Val_it =
-            _STD cbegin(_Data.values) + static_cast<_RANGES range_difference_t<const _MappedContainer>>(_Dist);
-        return const_iterator{_STD move(_Key_it), _STD move(_Val_it)};
+    template <class _SelfTy, class _KeyTy>
+    _NODISCARD auto _Lower_bound(this _SelfTy& _Self, const _KeyTy& _Key_val) {
+        return _Self._Find_bound(_Key_val, _RANGES lower_bound);
     }
 
-    template <class _KeyTy>
-    _NODISCARD pair<iterator, iterator> _Equal_range(const _KeyTy& _Key_val) {
-        _STL_INTERNAL_STATIC_ASSERT(is_same_v<_KeyTy, key_type> || _Transparent<key_compare>);
-        return {lower_bound(_Key_val), upper_bound(_Key_val)};
+    template <class _SelfTy, class _KeyTy>
+    _NODISCARD auto _Upper_bound(this _SelfTy& _Self, const _KeyTy& _Key_val) {
+        return _Self._Find_bound(_Key_val, _RANGES upper_bound);
     }
 
-    template <class _KeyTy>
-    _NODISCARD pair<const_iterator, const_iterator> _Equal_range(const _KeyTy& _Key_val) const {
+    template <class _SelfTy, class _KeyTy>
+    _NODISCARD auto _Equal_range(this _SelfTy& _Self, const _KeyTy& _Key_val) {
         _STL_INTERNAL_STATIC_ASSERT(is_same_v<_KeyTy, key_type> || _Transparent<key_compare>);
-        return {lower_bound(_Key_val), upper_bound(_Key_val)};
+        return pair{_Self.lower_bound(_Key_val), _Self.upper_bound(_Key_val)};
     }
 };
 
@@ -1399,22 +1351,11 @@ private:
     using _Mybase::_Key_equal;
     using _Mybase::_Pass_key_comp;
 
-    template <class _KeyTy>
-    _NODISCARD mapped_type& _At(const _KeyTy& _Key_val) {
-        _STL_INTERNAL_STATIC_ASSERT(is_same_v<_KeyTy, key_type> || _Transparent<key_compare>);
-        const auto _Position = this->find(_Key_val);
-        if (_Position == this->end()) {
-            _Xout_of_range("invalid flat_map key");
-        }
-
-        return _Position->second;
-    }
-
-    template <class _KeyTy>
-    _NODISCARD const mapped_type& _At(const _KeyTy& _Key_val) const {
+    template <class _SelfTy, class _KeyTy>
+    _NODISCARD auto& _At(this _SelfTy& _Self, const _KeyTy& _Key_val) {
         _STL_INTERNAL_STATIC_ASSERT(is_same_v<_KeyTy, key_type> || _Transparent<key_compare>);
-        const auto _Position = this->find(_Key_val);
-        if (_Position == this->end()) {
+        const auto _Position = _Self.find(_Key_val);
+        if (_Position == _Self.end()) {
             _Xout_of_range("invalid flat_map key");
         }
 
diff --git a/tests/std/tests/P0429R9_flat_map/test.cpp b/tests/std/tests/P0429R9_flat_map/test.cpp
index 74e88ddc81d..fac98c6ff64 100644
--- a/tests/std/tests/P0429R9_flat_map/test.cpp
+++ b/tests/std/tests/P0429R9_flat_map/test.cpp
@@ -766,6 +766,29 @@ void test_throwing_compare_swap() {
     test_throwing_compare_swap_single<flat_multimap, deque, deque>();
 }
 
+// Test that changes in GH-5987 did not break calls of lookup member functions by using deducing this.
+template <typename T>
+void test_lookup_call_on_temporaries_single() {
+    (void) T{}.lower_bound(42);
+    (void) T{}.lower_bound('a');
+    (void) T{}.upper_bound(42);
+    (void) T{}.upper_bound('a');
+    (void) T{}.equal_range(42);
+    (void) T{}.equal_range('a');
+    (void) T{}.find(42);
+    (void) T{}.find('a');
+}
+
+void test_lookup_call_on_temporaries() {
+    test_lookup_call_on_temporaries_single<flat_map<int, int>>();
+    test_lookup_call_on_temporaries_single<flat_multimap<int, int>>();
+    try {
+        (void) flat_map<int, int>{}.at(42);
+        (void) flat_map<int, int>{}.at('a');
+    } catch (...) {
+    }
+}
+
 int main() {
     test_construction();
     test_pointer_to_incomplete_type();
@@ -776,4 +799,5 @@ int main() {
     test_insert_or_assign();
     test_comparison();
     test_throwing_compare_swap();
+    test_lookup_call_on_temporaries();
 }