diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 11658b7..e3e5ea8 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -155,11 +155,10 @@ jobs:
             version: "*"
             cxx: "clang++"
             cc: "clang"
-            runs-on: "macos-11"
+            runs-on: "macos-14"
             b2-toolset: "clang"
             is-latest: true
-            is-earliest: true
-            name: "Apple-Clang"
+            name: "Apple-Clang (macOS 14)"
             build-type: "Release"
             build-cmake: true
 
@@ -167,10 +166,10 @@ jobs:
             version: "*"
             cxx: "clang++"
             cc: "clang"
-            runs-on: "macos-11"
+            runs-on: "macos-14"
             b2-toolset: "clang"
             is-latest: true
-            name: "Apple-Clang (ubsan)"
+            name: "Apple-Clang (macOS 14, ubsan)"
             build-type: "RelWithDebInfo"
             ubsan: true
 
@@ -178,123 +177,154 @@ jobs:
             version: "*"
             cxx: "clang++"
             cc: "clang"
-            runs-on: "macos-11"
+            runs-on: "macos-14"
             b2-toolset: "clang"
             is-latest: true
-            name: "Apple-Clang (asan)"
+            name: "Apple-Clang (macOS 14, asan)"
             build-type: "RelWithDebInfo"
             asan: true
 
+          - compiler: "apple-clang"
+            version: "*"
+            cxx: "clang++"
+            cc: "clang"
+            runs-on: "macos-13"
+            b2-toolset: "clang"
+            name: "Apple-Clang (macOS 13)"
+            build-type: "Release"
+
+          - compiler: "apple-clang"
+            version: "*"
+            cxx: "clang++"
+            cc: "clang"
+            runs-on: "macos-12"
+            b2-toolset: "clang"
+            name: "Apple-Clang (macOS 12)"
+            build-type: "Release"
+
           # Linux compilers
           #
 
           - compiler: "gcc"
-            version: "13"
+            version: "14"
             cxxstd: "17,20"
             latest-cxxstd: "20"
-            cxx: "g++-13"
-            cc: "gcc-13"
+            cxx: "g++-14"
+            cc: "gcc-14"
             runs-on: "ubuntu-latest"
-            container: "ubuntu:23.04"
+            container: "ubuntu:24.04"
             b2-toolset: "gcc"
             is-latest: true
-            name: "GCC 13: C++17-20"
+            name: "GCC 14: C++17-20"
             build-type: "Release"
             build-cmake: true
 
           - compiler: "gcc"
-            version: "13"
+            version: "14"
             cxxstd: "17,20"
             latest-cxxstd: "20"
-            cxx: "g++-13"
-            cc: "gcc-13"
+            cxx: "g++-14"
+            cc: "gcc-14"
             runs-on: "ubuntu-latest"
-            container: "ubuntu:23.04"
+            container: "ubuntu:24.04"
             b2-toolset: "gcc"
             is-latest: true
-            name: "GCC 13: C++17-20 (x86)"
+            name: "GCC 14: C++17-20 (x86)"
             x86: true
             build-type: "Release"
-            install: "gcc-13-multilib g++-13-multilib"
+            install: "gcc-14-multilib g++-14-multilib"
 
           - compiler: "gcc"
-            version: "13"
+            version: "14"
             cxxstd: "17,20"
             latest-cxxstd: "20"
-            cxx: "g++-13"
-            cc: "gcc-13"
+            cxx: "g++-14"
+            cc: "gcc-14"
             runs-on: "ubuntu-latest"
-            container: "ubuntu:23.04"
+            container: "ubuntu:24.04"
             b2-toolset: "gcc"
             is-latest: true
-            name: "GCC 13: C++17-20 (coverage)"
-            coverage: true
-            build-type: "Debug"
-            cxxflags: "--coverage -fprofile-arcs -ftest-coverage"
-            ccflags: "--coverage -fprofile-arcs -ftest-coverage"
-            install: "lcov wget unzip"
+            name: "GCC 14: C++17-20 (shared)"
+            shared: true
+            build-type: "Release"
+            build-cmake: true
 
           - compiler: "gcc"
-            version: "13"
+            version: "14"
             cxxstd: "17,20"
             latest-cxxstd: "20"
-            cxx: "g++-13"
-            cc: "gcc-13"
+            cxx: "g++-14"
+            cc: "gcc-14"
             runs-on: "ubuntu-latest"
-            container: "ubuntu:23.04"
+            container: "ubuntu:24.04"
             b2-toolset: "gcc"
             is-latest: true
-            name: "GCC 13: C++17-20 (shared)"
+            name: "GCC 14: C++17-20 (shared, x86)"
             shared: true
+            x86: true
             build-type: "Release"
+            install: "gcc-14-multilib g++-14-multilib"
             build-cmake: true
 
           - compiler: "gcc"
-            version: "13"
+            version: "14"
             cxxstd: "17,20"
             latest-cxxstd: "20"
-            cxx: "g++-13"
-            cc: "gcc-13"
+            cxx: "g++-14"
+            cc: "gcc-14"
             runs-on: "ubuntu-latest"
-            container: "ubuntu:23.04"
+            container: "ubuntu:24.04"
             b2-toolset: "gcc"
             is-latest: true
-            name: "GCC 13: C++17-20 (shared, x86)"
-            shared: true
-            x86: true
-            build-type: "Release"
-            install: "gcc-13-multilib g++-13-multilib"
-            build-cmake: true
+            name: "GCC 14: C++17-20 (asan)"
+            asan: true
+            build-type: "RelWithDebInfo"
 
           - compiler: "gcc"
-            version: "13"
+            version: "14"
             cxxstd: "17,20"
             latest-cxxstd: "20"
-            cxx: "g++-13"
-            cc: "gcc-13"
+            cxx: "g++-14"
+            cc: "gcc-14"
             runs-on: "ubuntu-latest"
-            container: "ubuntu:23.04"
+            container: "ubuntu:24.04"
             b2-toolset: "gcc"
             is-latest: true
-            name: "GCC 13: C++17-20 (asan)"
+            name: "GCC 14: C++17-20 (asan, x86)"
             asan: true
+            x86: true
             build-type: "RelWithDebInfo"
+            install: "gcc-14-multilib g++-14-multilib"
 
           - compiler: "gcc"
-            version: "13"
+            version: "14"
             cxxstd: "17,20"
             latest-cxxstd: "20"
-            cxx: "g++-13"
-            cc: "gcc-13"
+            cxx: "g++-14"
+            cc: "gcc-14"
             runs-on: "ubuntu-latest"
-            container: "ubuntu:23.04"
+            container: "ubuntu:24.04"
             b2-toolset: "gcc"
             is-latest: true
-            name: "GCC 13: C++17-20 (asan, x86)"
-            asan: true
+            name: "GCC 14: C++17-20 (ubsan)"
+            ubsan: true
+            build-type: "RelWithDebInfo"
+
+          - compiler: "gcc"
+            version: "14"
+            cxxstd: "17,20"
+            latest-cxxstd: "20"
+            cxx: "g++-14"
+            cc: "gcc-14"
+            runs-on: "ubuntu-latest"
+            container: "ubuntu:24.04"
+            b2-toolset: "gcc"
+            is-latest: true
+            name: "GCC 14: C++17-20 (ubsan, x86)"
+            ubsan: true
             x86: true
             build-type: "RelWithDebInfo"
-            install: "gcc-13-multilib g++-13-multilib"
+            install: "gcc-14-multilib g++-14-multilib"
 
           - compiler: "gcc"
             version: "13"
@@ -305,10 +335,8 @@ jobs:
             runs-on: "ubuntu-latest"
             container: "ubuntu:23.04"
             b2-toolset: "gcc"
-            is-latest: true
-            name: "GCC 13: C++17-20 (ubsan)"
-            ubsan: true
-            build-type: "RelWithDebInfo"
+            name: "GCC 13: C++17-20"
+            build-type: "Release"
 
           - compiler: "gcc"
             version: "13"
@@ -320,11 +348,12 @@ jobs:
             container: "ubuntu:23.04"
             b2-toolset: "gcc"
             is-latest: true
-            name: "GCC 13: C++17-20 (ubsan, x86)"
-            ubsan: true
-            x86: true
-            build-type: "RelWithDebInfo"
-            install: "gcc-13-multilib g++-13-multilib"
+            name: "GCC 13: C++17-20 (coverage)"
+            coverage: true
+            build-type: "Debug"
+            cxxflags: "--coverage -fprofile-arcs -ftest-coverage"
+            ccflags: "--coverage -fprofile-arcs -ftest-coverage"
+            install: "lcov wget unzip"
 
           - compiler: "gcc"
             version: "12"
@@ -424,45 +453,45 @@ jobs:
             build-type: "Release"
 
           - compiler: "clang"
-            version: "17"
+            version: "18"
             cxxstd: "17,20"
             latest-cxxstd: "20"
-            cxx: "clang++-17"
-            cc: "clang-17"
+            cxx: "clang++-18"
+            cc: "clang-18"
             runs-on: "ubuntu-latest"
-            container: "ubuntu:23.10"
+            container: "ubuntu:24.04"
             b2-toolset: "clang"
             is-latest: true
-            name: "Clang 17: C++17-20"
+            name: "Clang 18: C++17-20"
             build-type: "Release"
             build-cmake: true
 
           - compiler: "clang"
-            version: "17"
+            version: "18"
             cxxstd: "17,20"
             latest-cxxstd: "20"
-            cxx: "clang++-17"
-            cc: "clang-17"
+            cxx: "clang++-18"
+            cc: "clang-18"
             runs-on: "ubuntu-latest"
-            container: "ubuntu:23.10"
+            container: "ubuntu:24.04"
             b2-toolset: "clang"
             is-latest: true
-            name: "Clang 17: C++17-20 (x86)"
+            name: "Clang 18: C++17-20 (x86)"
             x86: true
             build-type: "Release"
             install: "gcc-multilib g++-multilib"
 
           - compiler: "clang"
-            version: "17"
+            version: "18"
             cxxstd: "20"
             latest-cxxstd: "20"
-            cxx: "clang++-17"
-            cc: "clang-17"
+            cxx: "clang++-18"
+            cc: "clang-18"
             runs-on: "ubuntu-latest"
-            container: "ubuntu:23.10"
+            container: "ubuntu:24.04"
             b2-toolset: "clang"
             is-latest: true
-            name: "Clang 17: C++20 (time-trace)"
+            name: "Clang 18: C++20 (time-trace)"
             time-trace: true
             build-type: "Release"
             cxxflags: "-ftime-trace"
@@ -470,65 +499,77 @@ jobs:
             install: "wget unzip"
 
           - compiler: "clang"
-            version: "17"
+            version: "18"
             cxxstd: "17,20"
             latest-cxxstd: "20"
-            cxx: "clang++-17"
-            cc: "clang-17"
+            cxx: "clang++-18"
+            cc: "clang-18"
             runs-on: "ubuntu-latest"
-            container: "ubuntu:23.10"
+            container: "ubuntu:24.04"
             b2-toolset: "clang"
             is-latest: true
-            name: "Clang 17: C++17-20 (asan)"
+            name: "Clang 18: C++17-20 (asan)"
             asan: true
             build-type: "RelWithDebInfo"
 
           - compiler: "clang"
-            version: "17"
+            version: "18"
             cxxstd: "17,20"
             latest-cxxstd: "20"
-            cxx: "clang++-17"
-            cc: "clang-17"
+            cxx: "clang++-18"
+            cc: "clang-18"
             runs-on: "ubuntu-latest"
-            container: "ubuntu:23.10"
+            container: "ubuntu:24.04"
             b2-toolset: "clang"
             is-latest: true
-            name: "Clang 17: C++17-20 (asan, x86)"
+            name: "Clang 18: C++17-20 (asan, x86)"
             asan: true
             x86: true
             build-type: "RelWithDebInfo"
             install: "gcc-multilib g++-multilib"
 
           - compiler: "clang"
-            version: "17"
+            version: "18"
             cxxstd: "17,20"
             latest-cxxstd: "20"
-            cxx: "clang++-17"
-            cc: "clang-17"
+            cxx: "clang++-18"
+            cc: "clang-18"
             runs-on: "ubuntu-latest"
-            container: "ubuntu:23.10"
+            container: "ubuntu:24.04"
             b2-toolset: "clang"
             is-latest: true
-            name: "Clang 17: C++17-20 (ubsan)"
+            name: "Clang 18: C++17-20 (ubsan)"
             ubsan: true
             build-type: "RelWithDebInfo"
 
           - compiler: "clang"
-            version: "17"
+            version: "18"
             cxxstd: "17,20"
             latest-cxxstd: "20"
-            cxx: "clang++-17"
-            cc: "clang-17"
+            cxx: "clang++-18"
+            cc: "clang-18"
             runs-on: "ubuntu-latest"
-            container: "ubuntu:23.10"
+            container: "ubuntu:24.04"
             b2-toolset: "clang"
             is-latest: true
-            name: "Clang 17: C++17-20 (ubsan, x86)"
+            name: "Clang 18: C++17-20 (ubsan, x86)"
             ubsan: true
             x86: true
             build-type: "RelWithDebInfo"
             install: "gcc-multilib g++-multilib"
 
+          - compiler: "clang"
+            version: "17"
+            cxxstd: "17,20"
+            latest-cxxstd: "20"
+            cxx: "clang++-17"
+            cc: "clang-17"
+            runs-on: "ubuntu-latest"
+            container: "ubuntu:23.10"
+            b2-toolset: "clang"
+            name: "Clang 17: C++17-20"
+            build-type: "Release"
+
           - compiler: "clang"
             version: "16"
             cxxstd: "17,20"
@@ -686,16 +727,16 @@ jobs:
             build-type: "Release"
 
           - compiler: "clang"
-            version: "^3.8"
+            version: "3.9"
             cxxstd: "11"
             latest-cxxstd: "11"
-            cxx: "clang++-3.8"
-            cc: "clang-3.8"
+            cxx: "clang++-3.9"
+            cc: "clang-3.9"
             runs-on: "ubuntu-latest"
-            container: "ubuntu:16.04"
+            container: "ubuntu:18.04"
             b2-toolset: "clang"
             is-earliest: true
-            name: "Clang ^3.8: C++11"
+            name: "Clang 3.9: C++11"
             build-type: "Release"
 
     name: ${{ matrix.name }}
@@ -704,6 +745,10 @@ jobs:
     timeout-minutes: 120
 
     steps:
+      - name: Enable Node 16
+        run: |
+          echo "ACTIONS_ALLOW_USE_UNSECURE_NODE_VERSION=true" >> $GITHUB_ENV
+
       - name: Clone Boost.Buffers
         uses: actions/checkout@v3
         with:
diff --git a/include/boost/buffers/flat_buffer.hpp b/include/boost/buffers/flat_buffer.hpp
index 46099e6..b7b00df 100644
--- a/include/boost/buffers/flat_buffer.hpp
+++ b/include/boost/buffers/flat_buffer.hpp
@@ -96,7 +96,7 @@ class flat_buffer
     std::size_t
     capacity() const noexcept
     {
-        return cap_ - in_pos_;
+        return cap_ - (in_pos_ + in_size_);
     }
 
     const_buffers_type
@@ -111,7 +111,7 @@ class flat_buffer
     prepare(std::size_t n)
     {
         // n exceeds available space
-        if(n > cap_ - in_size_)
+        if( n > capacity() )
             detail::throw_invalid_argument();
 
         out_size_ = n;
diff --git a/test/flat_buffer.cpp b/test/flat_buffer.cpp
index 16762e9..97956ae 100644
--- a/test/flat_buffer.cpp
+++ b/test/flat_buffer.cpp
@@ -51,7 +51,7 @@ struct flat_buffer_test
             flat_buffer fb(&s[0], s.size(), 6);
             BOOST_TEST_EQ(fb.size(), 6);
             BOOST_TEST_EQ(fb.max_size(), s.size());
-            BOOST_TEST_EQ(fb.capacity(), s.size());
+            BOOST_TEST_EQ(fb.capacity(), s.size() - 6);
         }
         {
             std::string s = pat;
@@ -78,7 +78,7 @@ struct flat_buffer_test
                 &s[0], s.size()), 6);
             BOOST_TEST_EQ(fb.size(), 6);
             BOOST_TEST_EQ(fb.max_size(), s.size());
-            BOOST_TEST_EQ(fb.capacity(), s.size());
+            BOOST_TEST_EQ(fb.capacity(), s.size() - 6);
         }
 
         // flat_buffer(flat_buffer const&)
@@ -110,6 +110,18 @@ struct flat_buffer_test
                 fb.prepare(s.size() + 1),
                 std::invalid_argument);
         }
+        {
+            std::string s = pat;
+            flat_buffer fb(&s[0], s.size(), 6);
+            BOOST_TEST_THROWS(
+                fb.prepare(s.size() + 1),
+                std::invalid_argument);
+
+            BOOST_TEST_EQ(fb.max_size(), s.size());
+            BOOST_TEST_EQ(
+                fb.size() + fb.capacity(),
+                fb.max_size());
+        }
 
         // commit(std::size_t)
         {
@@ -129,6 +141,38 @@ struct flat_buffer_test
 
         // consume(std::size_t)
         {
+            std::string s = pat;
+            flat_buffer fb(&s[0], s.size(), s.size());
+            BOOST_TEST_EQ(
+                test_to_string(fb.data()), pat);
+
+            auto const cap = fb.capacity();
+
+            while( fb.size() > 0 )
+            {
+                fb.prepare(fb.capacity());
+                fb.consume(1);
+
+                if( fb.size() > 0 )
+                    BOOST_TEST_EQ(fb.capacity(), cap);
+            }
+
+            BOOST_TEST_EQ(fb.capacity(), s.size());
+        }
+        {
+            std::string s = pat;
+            flat_buffer fb(&s[0], s.size(), 6);
+
+            auto const cap = fb.capacity();
+
+            BOOST_TEST_NO_THROW(
+                fb.prepare(fb.max_size() - fb.size()));
+
+            fb.consume(1);
+            BOOST_TEST_EQ(fb.capacity(), cap);
+            BOOST_TEST_THROWS(
+                fb.prepare(cap + 1),
+                std::invalid_argument);
         }
     }