diff --git a/.github/workflows/linux.yml b/.github/workflows/linux.yml
index 014e027b..6bced99b 100644
--- a/.github/workflows/linux.yml
+++ b/.github/workflows/linux.yml
@@ -33,6 +33,10 @@ jobs:
             std: 23
             install: sudo apt install g++-13
             shared: -DBUILD_SHARED_LIBS=ON
+          - cxx: g++-14
+            build_type: Release
+            std: 23
+            install: sudo apt install g++-14
           - cxx: clang++-11
             build_type: Debug
             std: 17
@@ -55,6 +59,11 @@ jobs:
             std: 20
             cxxflags: -stdlib=libc++
             install: sudo apt install libc++-14-dev libc++abi-14-dev
+          - cxx: clang++-20
+            build_type: Debug
+            std: 20
+            cxxflags: -stdlib=libc++
+            install: sudo apt install clang-20 libc++-20-dev libc++abi-20-dev
 
     steps:
     - uses: actions/checkout@1af3b93b6815bc44a9784bd300feb67ff0d1eeb3 # v6.0.0
@@ -131,7 +140,14 @@ jobs:
     - name: Add repositories for newer GCC
       run: |
         sudo apt-add-repository ppa:ubuntu-toolchain-r/test
-      if: ${{ matrix.cxx == 'g++-13' }}
+      if: ${{ matrix.cxx == 'g++-13' || matrix.cxx == 'g++-14' }}
+
+    - name: Install LLVM-20
+      run: |
+          wget https://apt.llvm.org/llvm.sh
+          chmod +x llvm.sh
+          sudo ./llvm.sh 20
+      if: ${{ matrix.cxx == 'clang++-20' }}
 
     - name: Add Ubuntu mirrors
       run: |
@@ -164,6 +180,23 @@ jobs:
               -DCMAKE_VISIBILITY_INLINES_HIDDEN=ON \
               -DFMT_DOC=OFF -DFMT_PEDANTIC=ON -DFMT_WERROR=ON \
               ${{matrix.fuzz}} ${{matrix.shared}} $GITHUB_WORKSPACE
+      if: ${{ matrix.cxx != 'clang++-20' && matrix.cxx != 'g++-14' }}
+
+    - name: Configure-Modules
+      working-directory: ${{runner.workspace}}/build
+      env:
+        CXX: ${{matrix.cxx}}
+        CXXFLAGS: ${{matrix.cxxflags}}
+      run: |
+        cmake -DCMAKE_BUILD_TYPE=${{matrix.build_type}} \
+              -DCMAKE_CXX_STANDARD=${{matrix.std}} \
+              -DCMAKE_CXX_EXTENSIONS=OFF \
+              -G Ninja \
+              -DCMAKE_CXX_VISIBILITY_PRESET=hidden \
+              -DCMAKE_VISIBILITY_INLINES_HIDDEN=ON \
+              -DFMT_DOC=OFF -DFMT_PEDANTIC=ON \
+              ${{matrix.fuzz}} ${{matrix.shared}} $GITHUB_WORKSPACE
+      if: ${{ matrix.cxx == 'clang++-20' || matrix.cxx == 'g++-14' }}
 
     - name: Build
       working-directory: ${{runner.workspace}}/build
diff --git a/include/fmt/base.h b/include/fmt/base.h
index bf9347e0..3c629859 100644
--- a/include/fmt/base.h
+++ b/include/fmt/base.h
@@ -1859,42 +1859,38 @@ class fixed_buffer_traits {
 };
 
 template <typename OutputIt, typename InputIt, typename = void>
-struct has_back_insert_iterator_container_append : std::false_type {};
+struct has_append : std::false_type {};
 
 template <typename OutputIt, typename InputIt>
-struct has_back_insert_iterator_container_append<
-    OutputIt, InputIt,
-    void_t<decltype(get_container(std::declval<OutputIt>())
-                        .append(std::declval<InputIt>(),
-                                std::declval<InputIt>()))>> : std::true_type {};
+struct has_append<OutputIt, InputIt,
+                  void_t<decltype(get_container(std::declval<OutputIt>())
+                                      .append(std::declval<InputIt>(),
+                                              std::declval<InputIt>()))>>
+    : std::true_type {};
 
-template <typename OutputIt, typename InputIt, typename = void>
-struct has_back_insert_iterator_container_insert_at_end : std::false_type {};
+template <typename OutputIt, typename T, typename = void>
+struct has_insert : std::false_type {};
 
-template <typename OutputIt, typename InputIt>
-struct has_back_insert_iterator_container_insert_at_end<
-    OutputIt, InputIt,
-    void_t<decltype(get_container(std::declval<OutputIt>())
-                        .insert(get_container(std::declval<OutputIt>()).end(),
-                                std::declval<InputIt>(),
-                                std::declval<InputIt>()))>> : std::true_type {};
+template <typename OutputIt, typename T>
+struct has_insert<OutputIt, T,
+                  void_t<decltype(get_container(std::declval<OutputIt>())
+                                      .insert({}, std::declval<T>(),
+                                              std::declval<T>()))>>
+    : std::true_type {};
 
 // An optimized version of std::copy with the output value type (T).
 template <typename T, typename InputIt, typename OutputIt,
-          FMT_ENABLE_IF(is_back_insert_iterator<OutputIt>::value&&
-                            has_back_insert_iterator_container_append<
-                                OutputIt, InputIt>::value)>
+          FMT_ENABLE_IF(is_back_insert_iterator<OutputIt>() &&
+                        has_append<OutputIt, InputIt>())>
 FMT_CONSTEXPR auto copy(InputIt begin, InputIt end, OutputIt out) -> OutputIt {
   get_container(out).append(begin, end);
   return out;
 }
 
 template <typename T, typename InputIt, typename OutputIt,
-          FMT_ENABLE_IF(is_back_insert_iterator<OutputIt>::value &&
-                        !has_back_insert_iterator_container_append<
-                            OutputIt, InputIt>::value &&
-                        has_back_insert_iterator_container_insert_at_end<
-                            OutputIt, InputIt>::value)>
+          FMT_ENABLE_IF(is_back_insert_iterator<OutputIt>() &&
+                        !has_append<OutputIt, InputIt>() &&
+                        has_insert<OutputIt, InputIt>())>
 FMT_CONSTEXPR auto copy(InputIt begin, InputIt end, OutputIt out) -> OutputIt {
   auto& c = get_container(out);
   c.insert(c.end(), begin, end);
@@ -1902,21 +1898,14 @@ FMT_CONSTEXPR auto copy(InputIt begin, InputIt end, OutputIt out) -> OutputIt {
 }
 
 template <typename T, typename InputIt, typename OutputIt,
-          FMT_ENABLE_IF(!(is_back_insert_iterator<OutputIt>::value &&
-                          (has_back_insert_iterator_container_append<
-                               OutputIt, InputIt>::value ||
-                           has_back_insert_iterator_container_insert_at_end<
-                               OutputIt, InputIt>::value)))>
+          FMT_ENABLE_IF(!is_back_insert_iterator<OutputIt>() ||
+                        !(has_append<OutputIt, InputIt>() ||
+                          has_insert<OutputIt, InputIt>()))>
 FMT_CONSTEXPR auto copy(InputIt begin, InputIt end, OutputIt out) -> OutputIt {
   while (begin != end) *out++ = static_cast<T>(*begin++);
   return out;
 }
 
-template <typename T, typename V, typename OutputIt>
-FMT_CONSTEXPR auto copy(basic_string_view<V> s, OutputIt out) -> OutputIt {
-  return copy<T>(s.begin(), s.end(), out);
-}
-
 // A buffer that writes to an output iterator when flushed.
 template <typename OutputIt, typename T, typename Traits = buffer_traits>
 class iterator_buffer : public Traits, public buffer<T> {
@@ -1934,12 +1923,7 @@ class iterator_buffer : public Traits, public buffer<T> {
     this->clear();
     const T* begin = data_;
     const T* end = begin + this->limit(size);
-#if defined(__cpp_if_constexpr)
-    if constexpr (std::is_move_assignable<OutputIt>::value)
-      out_ = copy<T>(begin, end, out_);
-    else
-#endif
-      while (begin != end) *out_++ = *begin++;
+    out_ = copy<T>(begin, end, out_);
   }
 
  public:
diff --git a/include/fmt/format.h b/include/fmt/format.h
index c93d85ac..96c21329 100644
--- a/include/fmt/format.h
+++ b/include/fmt/format.h
@@ -548,6 +548,11 @@ FMT_CONSTEXPR20 auto fill_n(T* out, Size count, char value) -> T* {
   return out + count;
 }
 
+template <typename T, typename V, typename OutputIt>
+FMT_CONSTEXPR auto copy(basic_string_view<V> s, OutputIt out) -> OutputIt {
+  return copy<T>(s.begin(), s.end(), out);
+}
+
 template <typename OutChar, typename InputIt, typename OutputIt>
 FMT_CONSTEXPR FMT_NOINLINE auto copy_noinline(InputIt begin, InputIt end,
                                               OutputIt out) -> OutputIt {
diff --git a/test/base-test.cc b/test/base-test.cc
index bf268875..9575e055 100644
--- a/test/base-test.cc
+++ b/test/base-test.cc
@@ -811,10 +811,10 @@ TEST(base_test, throw_in_buffer_dtor) {
   constexpr int buffer_size = 256;
 
   struct throwing_iterator {
-    int& count;
+    int* count;
 
     auto operator=(char) -> throwing_iterator& {
-      if (++count > buffer_size) throw std::exception();
+      if (++*count > buffer_size) throw std::exception();
       return *this;
     }
     auto operator*() -> throwing_iterator& { return *this; }
@@ -824,7 +824,7 @@ TEST(base_test, throw_in_buffer_dtor) {
 
   try {
     int count = 0;
-    fmt::format_to(throwing_iterator{count}, fmt::runtime("{:{}}{"), "",
+    fmt::format_to(throwing_iterator{&count}, fmt::runtime("{:{}}{"), "",
                    buffer_size + 1);
   } catch (const std::exception&) {
   }