diff --git a/libstdc++-v3/include/bits/stl_algo.h b/libstdc++-v3/include/bits/stl_algo.h
index 7a0cf6b6737..bbc130d3e71 100644
--- a/libstdc++-v3/include/bits/stl_algo.h
+++ b/libstdc++-v3/include/bits/stl_algo.h
@@ -320,7 +320,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  [__first1,__last1-(__last2-__first2))
   */
   template<typename _ForwardIterator1, typename _ForwardIterator2>
-    _GLIBCXX20_CONSTEXPR
+    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
     inline _ForwardIterator1
     find_end(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
 	     _ForwardIterator2 __first2, _ForwardIterator2 __last2)
@@ -370,7 +370,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   */
   template<typename _ForwardIterator1, typename _ForwardIterator2,
 	   typename _BinaryPredicate>
-    _GLIBCXX20_CONSTEXPR
+    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
     inline _ForwardIterator1
     find_end(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
 	     _ForwardIterator2 __first2, _ForwardIterator2 __last2,
@@ -405,7 +405,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  @p [__first,__last), and false otherwise.
   */
   template<typename _InputIterator, typename _Predicate>
-    _GLIBCXX20_CONSTEXPR
+    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
     inline bool
     all_of(_InputIterator __first, _InputIterator __last, _Predicate __pred)
     { return __last == std::find_if_not(__first, __last, __pred); }
@@ -423,7 +423,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  @p [__first,__last), and false otherwise.
   */
   template<typename _InputIterator, typename _Predicate>
-    _GLIBCXX20_CONSTEXPR
+    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
     inline bool
     none_of(_InputIterator __first, _InputIterator __last, _Predicate __pred)
     { return __last == _GLIBCXX_STD_A::find_if(__first, __last, __pred); }
@@ -442,7 +442,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  otherwise.
   */
   template<typename _InputIterator, typename _Predicate>
-    _GLIBCXX20_CONSTEXPR
+    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
     inline bool
     any_of(_InputIterator __first, _InputIterator __last, _Predicate __pred)
     { return !std::none_of(__first, __last, __pred); }
@@ -458,7 +458,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  such that @p __pred(*i) is false, or @p __last if no such iterator exists.
   */
   template<typename _InputIterator, typename _Predicate>
-    _GLIBCXX20_CONSTEXPR
+    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
     inline _InputIterator
     find_if_not(_InputIterator __first, _InputIterator __last,
 		_Predicate __pred)
@@ -483,7 +483,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  do not.
   */
   template<typename _InputIterator, typename _Predicate>
-    _GLIBCXX20_CONSTEXPR
+    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
     inline bool
     is_partitioned(_InputIterator __first, _InputIterator __last,
 		   _Predicate __pred)
@@ -505,7 +505,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *           and @p none_of(mid, __last, __pred) are both true.
   */
   template<typename _ForwardIterator, typename _Predicate>
-    _GLIBCXX20_CONSTEXPR
+    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
     _ForwardIterator
     partition_point(_ForwardIterator __first, _ForwardIterator __last,
 		    _Predicate __pred)
@@ -572,7 +572,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  are copied is unchanged.
   */
   template<typename _InputIterator, typename _OutputIterator, typename _Tp>
-    _GLIBCXX20_CONSTEXPR
+    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
     inline _OutputIterator
     remove_copy(_InputIterator __first, _InputIterator __last,
 		_OutputIterator __result, const _Tp& __value)
@@ -606,7 +606,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   */
   template<typename _InputIterator, typename _OutputIterator,
 	   typename _Predicate>
-    _GLIBCXX20_CONSTEXPR
+    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
     inline _OutputIterator
     remove_copy_if(_InputIterator __first, _InputIterator __last,
 		   _OutputIterator __result, _Predicate __pred)
@@ -783,7 +783,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  are still present, but their value is unspecified.
   */
   template<typename _ForwardIterator, typename _Tp>
-    _GLIBCXX20_CONSTEXPR
+    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
     inline _ForwardIterator
     remove(_ForwardIterator __first, _ForwardIterator __last,
 	   const _Tp& __value)
@@ -817,7 +817,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  are still present, but their value is unspecified.
   */
   template<typename _ForwardIterator, typename _Predicate>
-    _GLIBCXX20_CONSTEXPR
+    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
     inline _ForwardIterator
     remove_if(_ForwardIterator __first, _ForwardIterator __last,
 	      _Predicate __pred)
@@ -886,7 +886,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  are still present, but their value is unspecified.
   */
   template<typename _ForwardIterator>
-    _GLIBCXX20_CONSTEXPR
+    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
     inline _ForwardIterator
     unique(_ForwardIterator __first, _ForwardIterator __last)
     {
@@ -917,7 +917,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  are still present, but their value is unspecified.
   */
   template<typename _ForwardIterator, typename _BinaryPredicate>
-    _GLIBCXX20_CONSTEXPR
+    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
     inline _ForwardIterator
     unique(_ForwardIterator __first, _ForwardIterator __last,
 	   _BinaryPredicate __binary_pred)
@@ -4019,7 +4019,7 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
    *  for which @c *i == @p __value
   */
   template<typename _InputIterator, typename _Tp>
-    _GLIBCXX20_CONSTEXPR
+    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
     inline typename iterator_traits<_InputIterator>::difference_type
     count(_InputIterator __first, _InputIterator __last, const _Tp& __value)
     {
@@ -4043,7 +4043,7 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
    *  for which @p __pred(*i) is true.
   */
   template<typename _InputIterator, typename _Predicate>
-    _GLIBCXX20_CONSTEXPR
+    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
     inline typename iterator_traits<_InputIterator>::difference_type
     count_if(_InputIterator __first, _InputIterator __last, _Predicate __pred)
     {
@@ -4118,7 +4118,7 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
    *  equal to @p __val.
   */
   template<typename _ForwardIterator, typename _Integer, typename _Tp>
-    _GLIBCXX20_CONSTEXPR
+    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
     inline _ForwardIterator
     search_n(_ForwardIterator __first, _ForwardIterator __last,
 	     _Integer __count, const _Tp& __val)
@@ -4407,7 +4407,7 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
   // DR 538. 241 again: Does unique_copy() require CopyConstructible and
   // Assignable?
   template<typename _InputIterator, typename _OutputIterator>
-    _GLIBCXX20_CONSTEXPR
+    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
     inline _OutputIterator
     unique_copy(_InputIterator __first, _InputIterator __last,
 		_OutputIterator __result)
@@ -4448,7 +4448,7 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
   // DR 241. Does unique_copy() require CopyConstructible and Assignable?
   template<typename _InputIterator, typename _OutputIterator,
 	   typename _BinaryPredicate>
-    _GLIBCXX20_CONSTEXPR
+    _GLIBCXX_NODISCARD _GLIBCXX20_CONSTEXPR
     inline _OutputIterator
     unique_copy(_InputIterator __first, _InputIterator __last,
 		_OutputIterator __result,
diff --git a/libstdc++-v3/testsuite/25_algorithms/unique/1.cc b/libstdc++-v3/testsuite/25_algorithms/unique/1.cc
index 6826e26fdc0..698c370e229 100644
--- a/libstdc++-v3/testsuite/25_algorithms/unique/1.cc
+++ b/libstdc++-v3/testsuite/25_algorithms/unique/1.cc
@@ -27,5 +27,6 @@ int main()
   using namespace std;
   list<int> menge;
   unique (menge.begin(), menge.end());
+  // { dg-warning "ignoring return value" "" { target c++17 } 29 }
   return 0;
 }
diff --git a/libstdc++-v3/testsuite/25_algorithms/unique/11480.cc b/libstdc++-v3/testsuite/25_algorithms/unique/11480.cc
index 9d1bd4efe32..a008fc57f54 100644
--- a/libstdc++-v3/testsuite/25_algorithms/unique/11480.cc
+++ b/libstdc++-v3/testsuite/25_algorithms/unique/11480.cc
@@ -31,7 +31,7 @@ bool compare(int a, int b)
 // libstdc++/11480
 void test01()
 {
-  std::unique(a, a+10, compare);
+  std::unique(a, a+10, compare); // { dg-warning "ignoring return value" "" { target c++17 } }
   VERIFY( compare_count == 9 );
 }
 
diff --git a/libstdc++-v3/testsuite/25_algorithms/unique_copy/26133.cc b/libstdc++-v3/testsuite/25_algorithms/unique_copy/26133.cc
index 9f9a26e0dd4..482a610f53c 100644
--- a/libstdc++-v3/testsuite/25_algorithms/unique_copy/26133.cc
+++ b/libstdc++-v3/testsuite/25_algorithms/unique_copy/26133.cc
@@ -35,10 +35,12 @@ void test01()
   no_assign in[4];
 
   std::unique_copy(in, in + 4, std::ostream_iterator<int>(oss1, "\n"));
+  // { dg-warning "ignoring return value" "" { target c++17 } 37 }
   VERIFY( oss1.str() == "23\n" );
 
   std::unique_copy(in, in + 4, std::ostream_iterator<int>(oss2, "\n"),
 		   std::equal_to<int>());
+  // { dg-warning "ignoring return value" "" { target c++17 } 41 }
   VERIFY( oss2.str() == "23\n" );
 }
 
