diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 4abc4b78..86347af4 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -81,7 +81,6 @@ jobs:
               compiler: clang-12,  cxxstd: '03,11,14,17,20', os: ubuntu-20.04, stdlib: libc++, install: 'clang-12 libc++-12-dev libc++abi-12-dev' }
 
           # OSX, clang
-          - { compiler: clang,     cxxstd: '03,11,14,17,2a',    os: macos-11 }
           - { compiler: clang,     cxxstd: '03,11,14,17,20',    os: macos-12 }
           - { name: MacOS w/ clang and sanitizers,
               compiler: clang,     cxxstd: '03,11,14,17,20,2b', os: macos-13, sanitize: yes }
diff --git a/CMakeLists.txt b/CMakeLists.txt
index fd2899cd..301880e2 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -18,7 +18,6 @@ target_link_libraries(boost_numeric_odeint
     Boost::compute
     Boost::config
     Boost::core
-    Boost::function
     Boost::fusion
     Boost::iterator
     Boost::math
diff --git a/include/boost/numeric/odeint/integrate/observer_collection.hpp b/include/boost/numeric/odeint/integrate/observer_collection.hpp
index f8c9af8e..4c4949a1 100644
--- a/include/boost/numeric/odeint/integrate/observer_collection.hpp
+++ b/include/boost/numeric/odeint/integrate/observer_collection.hpp
@@ -19,8 +19,7 @@
 #define BOOST_NUMERIC_ODEINT_INTEGRATE_OBSERVER_COLLECTION_HPP_INCLUDED
 
 #include <vector>
-
-#include <boost/function.hpp>
+#include <functional>
 
 namespace boost {
 namespace numeric {
@@ -31,7 +30,7 @@ class observer_collection
 {
 public:
 
-    typedef boost::function< void( const State& , const Time& ) > observer_type;
+    typedef std::function< void( const State& , const Time& ) > observer_type;
     typedef std::vector< observer_type > collection_type;
 
     void operator()( const State& x , Time t )
diff --git a/include/boost/numeric/odeint/iterator/integrate/observer_collection.hpp b/include/boost/numeric/odeint/iterator/integrate/observer_collection.hpp
index 26101a3a..8c40378b 100644
--- a/include/boost/numeric/odeint/iterator/integrate/observer_collection.hpp
+++ b/include/boost/numeric/odeint/iterator/integrate/observer_collection.hpp
@@ -19,8 +19,7 @@
 #define BOOST_NUMERIC_ODEINT_INTEGRATE_OBSERVER_COLLECTION_HPP_INCLUDED
 
 #include <vector>
-
-#include <boost/function.hpp>
+#include <functional>
 
 namespace boost {
 namespace numeric {
@@ -31,7 +30,7 @@ class observer_collection
 {
 public:
 
-    typedef boost::function< void( const State& , const Time& ) > observer_type;
+    typedef std::function< void( const State& , const Time& ) > observer_type;
     typedef std::vector< observer_type > collection_type;
 
     void operator()( const State& x , Time t )