diff --git a/libcxx/include/__new/global_new_delete.h b/libcxx/include/__new/global_new_delete.h
index 7d0797e4832467..96510ab56b00b5 100644
--- a/libcxx/include/__new/global_new_delete.h
+++ b/libcxx/include/__new/global_new_delete.h
@@ -26,18 +26,6 @@
 #endif
 
 #if defined(__cpp_sized_deallocation) && __cpp_sized_deallocation >= 201309L
-#  define _LIBCPP_HAS_LANGUAGE_SIZED_DEALLOCATION 1
-#else
-#  define _LIBCPP_HAS_LANGUAGE_SIZED_DEALLOCATION 0
-#endif
-
-#if _LIBCPP_STD_VER >= 14 || _LIBCPP_HAS_LANGUAGE_SIZED_DEALLOCATION
-#  define _LIBCPP_HAS_LIBRARY_SIZED_DEALLOCATION 1
-#else
-#  define _LIBCPP_HAS_LIBRARY_SIZED_DEALLOCATION 0
-#endif
-
-#if _LIBCPP_HAS_LIBRARY_SIZED_DEALLOCATION && _LIBCPP_HAS_LANGUAGE_SIZED_DEALLOCATION
 #  define _LIBCPP_HAS_SIZED_DEALLOCATION 1
 #else
 #  define _LIBCPP_HAS_SIZED_DEALLOCATION 0
@@ -51,7 +39,7 @@
     _LIBCPP_NOALIAS;
 _LIBCPP_OVERRIDABLE_FUNC_VIS void operator delete(void* __p) _NOEXCEPT;
 _LIBCPP_OVERRIDABLE_FUNC_VIS void operator delete(void* __p, const std::nothrow_t&) _NOEXCEPT;
-#  if _LIBCPP_HAS_LIBRARY_SIZED_DEALLOCATION
+#  if _LIBCPP_HAS_SIZED_DEALLOCATION
 _LIBCPP_OVERRIDABLE_FUNC_VIS void operator delete(void* __p, std::size_t __sz) _NOEXCEPT;
 #  endif
 
@@ -60,7 +48,7 @@ _LIBCPP_OVERRIDABLE_FUNC_VIS void operator delete(void* __p, std::size_t __sz) _
     _LIBCPP_NOALIAS;
 _LIBCPP_OVERRIDABLE_FUNC_VIS void operator delete[](void* __p) _NOEXCEPT;
 _LIBCPP_OVERRIDABLE_FUNC_VIS void operator delete[](void* __p, const std::nothrow_t&) _NOEXCEPT;
-#  if _LIBCPP_HAS_LIBRARY_SIZED_DEALLOCATION
+#  if _LIBCPP_HAS_SIZED_DEALLOCATION
 _LIBCPP_OVERRIDABLE_FUNC_VIS void operator delete[](void* __p, std::size_t __sz) _NOEXCEPT;
 #  endif
 
@@ -70,7 +58,7 @@ _LIBCPP_OVERRIDABLE_FUNC_VIS void operator delete[](void* __p, std::size_t __sz)
 operator new(std::size_t __sz, std::align_val_t, const std::nothrow_t&) _NOEXCEPT _LIBCPP_NOALIAS;
 _LIBCPP_OVERRIDABLE_FUNC_VIS void operator delete(void* __p, std::align_val_t) _NOEXCEPT;
 _LIBCPP_OVERRIDABLE_FUNC_VIS void operator delete(void* __p, std::align_val_t, const std::nothrow_t&) _NOEXCEPT;
-#    if _LIBCPP_HAS_LIBRARY_SIZED_DEALLOCATION
+#    if _LIBCPP_HAS_SIZED_DEALLOCATION
 _LIBCPP_OVERRIDABLE_FUNC_VIS void operator delete(void* __p, std::size_t __sz, std::align_val_t) _NOEXCEPT;
 #    endif
 
@@ -80,7 +68,7 @@ operator new[](std::size_t __sz, std::align_val_t) _THROW_BAD_ALLOC;
 operator new[](std::size_t __sz, std::align_val_t, const std::nothrow_t&) _NOEXCEPT _LIBCPP_NOALIAS;
 _LIBCPP_OVERRIDABLE_FUNC_VIS void operator delete[](void* __p, std::align_val_t) _NOEXCEPT;
 _LIBCPP_OVERRIDABLE_FUNC_VIS void operator delete[](void* __p, std::align_val_t, const std::nothrow_t&) _NOEXCEPT;
-#    if _LIBCPP_HAS_LIBRARY_SIZED_DEALLOCATION
+#    if _LIBCPP_HAS_SIZED_DEALLOCATION
 _LIBCPP_OVERRIDABLE_FUNC_VIS void operator delete[](void* __p, std::size_t __sz, std::align_val_t) _NOEXCEPT;
 #    endif
 #  endif
diff --git a/libcxxabi/src/CMakeLists.txt b/libcxxabi/src/CMakeLists.txt
index 21dda44e09976a..0a6fc892a4f699 100644
--- a/libcxxabi/src/CMakeLists.txt
+++ b/libcxxabi/src/CMakeLists.txt
@@ -77,7 +77,7 @@ endif()
 
 if (FUCHSIA)
     # TODO: Use CMAKE_LINK_LIBRARY_USING_FEATURE once our minimum CMake is at least 3.24
-    # https://cmake.org/cmake/help/latest/variable/CMAKE_LINK_LIBRARY_USING_FEATURE.html 
+    # https://cmake.org/cmake/help/latest/variable/CMAKE_LINK_LIBRARY_USING_FEATURE.html
     add_link_flags("-Wl,--push-state,--as-needed,-lzircon,--pop-state")
 endif()
 
@@ -190,6 +190,10 @@ if (CMAKE_POSITION_INDEPENDENT_CODE OR NOT DEFINED CMAKE_POSITION_INDEPENDENT_CO
 endif()
 target_compile_options(cxxabi_shared_objects PRIVATE "${LIBCXXABI_ADDITIONAL_COMPILE_FLAGS}")
 
+# Build with -fsized-deallocation, which is default in recent versions of Clang.
+# TODO(LLVM 21): This can be dropped once we only support Clang >= 19.
+target_add_compile_flags_if_supported(cxxabi_shared_objects PRIVATE -fsized-deallocation)
+
 add_library(cxxabi_shared SHARED)
 set_target_properties(cxxabi_shared
   PROPERTIES
@@ -281,6 +285,10 @@ set_target_properties(cxxabi_static_objects
 )
 target_compile_options(cxxabi_static_objects PRIVATE "${LIBCXXABI_ADDITIONAL_COMPILE_FLAGS}")
 
+# Build with -fsized-deallocation, which is default in recent versions of Clang.
+# TODO(LLVM 21): This can be dropped once we only support Clang >= 19.
+target_add_compile_flags_if_supported(cxxabi_static_objects PRIVATE -fsized-deallocation)
+
 if(LIBCXXABI_HERMETIC_STATIC_LIBRARY)
   target_add_compile_flags_if_supported(cxxabi_static_objects PRIVATE -fvisibility=hidden)
   # If the hermetic library doesn't define the operator new/delete functions