diff --git a/ACE/ace/Auto_Ptr.h b/ACE/ace/Auto_Ptr.h
index 43b704e02bbf8..8ac2d98d603d3 100644
--- a/ACE/ace/Auto_Ptr.h
+++ b/ACE/ace/Auto_Ptr.h
@@ -68,9 +68,14 @@ class ACE_Auto_Basic_Ptr
 
 ACE_END_VERSIONED_NAMESPACE_DECL
 
+// NOTE: ACE7 and TAO3 require C++11 support or newer; jwillemsen commented on Jun 1, 2021
+#if defined (ACE_LACKS_AUTO_PTR)
+#  undef ACE_LACKS_AUTO_PTR
+#endif
+
 #if !defined (ACE_LACKS_AUTO_PTR)
-#include <memory>
-using std::auto_ptr;
+#  include <memory>
+// NO! using std::unique_ptr;
 #else /* !ACE_LACKS_AUTO_PTR */
 
 ACE_BEGIN_VERSIONED_NAMESPACE_DECL
diff --git a/ACE/tests/Reactor_Remove_Resume_Test_Dev_Poll.cpp b/ACE/tests/Reactor_Remove_Resume_Test_Dev_Poll.cpp
index e591a9b015931..61a46779914d2 100644
--- a/ACE/tests/Reactor_Remove_Resume_Test_Dev_Poll.cpp
+++ b/ACE/tests/Reactor_Remove_Resume_Test_Dev_Poll.cpp
@@ -375,7 +375,7 @@ dev_poll_reactor_factory ()
  *
  * Reactor test execution functor.
  */
-struct Run_Test : public std::unary_function<reactor_factory_type, void>
+struct Run_Test : public std::function<void(reactor_factory_type)>
 {
   /// Function call operator overload.
   void operator() (reactor_factory_type factory)
diff --git a/TAO/tests/Any/Recursive/client.cpp b/TAO/tests/Any/Recursive/client.cpp
index 142d5ac6e53dc..e030acbe37695 100644
--- a/TAO/tests/Any/Recursive/client.cpp
+++ b/TAO/tests/Any/Recursive/client.cpp
@@ -399,7 +399,7 @@ directly_recursive_valuetype_typecodefactory_test (CORBA::ORB_ptr /* orb */,
  * Test method invocation functor.
  */
 template <typename T>
-struct Caller : public std::unary_function<T, void>
+struct Caller : public std::function<void(T)>
 {
   /// Constructor.
   Caller (CORBA::ORB_ptr o, Test::Hello_ptr h)
diff --git a/TAO/tests/Bug_2804_Regression/client.cpp b/TAO/tests/Bug_2804_Regression/client.cpp
index d852e043aa653..abee937b71120 100644
--- a/TAO/tests/Bug_2804_Regression/client.cpp
+++ b/TAO/tests/Bug_2804_Regression/client.cpp
@@ -97,7 +97,7 @@ recursive_union_test (CORBA::ORB_ptr /* orb */,
  * Test method invocation functor.
  */
 template <typename T>
-struct Caller : public std::unary_function<T, void>
+struct Caller : public std::function<void(T)>
 {
   /// Constructor.
   Caller (CORBA::ORB_ptr o, Test::Hello_ptr h)
diff --git a/TAO/tests/Bug_2844_Regression/client.cpp b/TAO/tests/Bug_2844_Regression/client.cpp
index 29fe9fa32c282..7021b6ff0d991 100644
--- a/TAO/tests/Bug_2844_Regression/client.cpp
+++ b/TAO/tests/Bug_2844_Regression/client.cpp
@@ -96,7 +96,7 @@ nested_recursive_struct_test (CORBA::ORB_ptr /* orb */,
  * Test method invocation functor.
  */
 template <typename T>
-struct Caller : public std::unary_function<T, void>
+struct Caller : public std::function<void(T)>
 {
   /// Constructor.
   Caller (CORBA::ORB_ptr o, Test::Hello_ptr h)
diff --git a/TAO/tests/Bug_2918_Regression/client.cpp b/TAO/tests/Bug_2918_Regression/client.cpp
index 14f608c2f68b3..7a4d6ed1b5e01 100644
--- a/TAO/tests/Bug_2918_Regression/client.cpp
+++ b/TAO/tests/Bug_2918_Regression/client.cpp
@@ -97,7 +97,7 @@ repeated_struct_test (CORBA::ORB_ptr /* orb */,
  * Test method invocation functor.
  */
 template <typename T>
-struct Caller : public std::unary_function<T, void>
+struct Caller : public std::function<void(T)>
 {
   /// Constructor.
   Caller (CORBA::ORB_ptr o, Test::Hello_ptr h)
diff --git a/TAO/tests/Bug_3919_Regression/client.cpp b/TAO/tests/Bug_3919_Regression/client.cpp
index 959d9b79f0162..83e67ab411b6e 100644
--- a/TAO/tests/Bug_3919_Regression/client.cpp
+++ b/TAO/tests/Bug_3919_Regression/client.cpp
@@ -168,7 +168,7 @@ nested_recursive_typecode_test (CORBA::ORB_ptr /* orb */,
  * Test method invocation functor.
  */
 template <typename T>
-struct Caller : public std::unary_function<T, void>
+struct Caller : public std::function<void(T)>
 {
   /// Constructor.
   Caller (CORBA::ORB_ptr o, Test::Hello_ptr h)