diff --git a/libcxx/include/CMakeLists.txt b/libcxx/include/CMakeLists.txt
--- a/libcxx/include/CMakeLists.txt
+++ b/libcxx/include/CMakeLists.txt
@@ -41,7 +41,6 @@
   __ranges/view.h
   __ranges/size.h
   __split_buffer
-  __sso_allocator
   __std_stream
   __string
   __threading_support
diff --git a/libcxx/include/module.modulemap b/libcxx/include/module.modulemap
--- a/libcxx/include/module.modulemap
+++ b/libcxx/include/module.modulemap
@@ -542,7 +542,6 @@
   module __locale { header "__locale" export * }
   module __mutex_base { header "__mutex_base" export * }
   module __split_buffer { header "__split_buffer" export * }
-  module __sso_allocator { header "__sso_allocator" export * }
   module __std_stream { header "__std_stream" export * }
   module __string { header "__string" export * }
   module __tree { header "__tree" export * }
diff --git a/libcxx/src/CMakeLists.txt b/libcxx/src/CMakeLists.txt
--- a/libcxx/src/CMakeLists.txt
+++ b/libcxx/src/CMakeLists.txt
@@ -64,6 +64,7 @@
 
 if (LIBCXX_ENABLE_LOCALIZATION)
   list(APPEND LIBCXX_SOURCES
+    include/sso_allocator.h
     ios.cpp
     ios.instantiations.cpp
     iostream.cpp
diff --git a/libcxx/include/__sso_allocator b/libcxx/src/include/sso_allocator.h
rename from libcxx/include/__sso_allocator
rename to libcxx/src/include/sso_allocator.h
--- a/libcxx/include/__sso_allocator
+++ b/libcxx/src/include/sso_allocator.h
@@ -7,8 +7,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef _LIBCPP___SSO_ALLOCATOR
-#define _LIBCPP___SSO_ALLOCATOR
+#ifndef _LIBCPP_SSO_ALLOCATOR_H
+#define _LIBCPP_SSO_ALLOCATOR_H
 
 #include <__config>
 #include <memory>
@@ -67,11 +67,11 @@
     _LIBCPP_INLINE_VISIBILITY size_type max_size() const throw() {return size_type(~0) / sizeof(_Tp);}
 
     _LIBCPP_INLINE_VISIBILITY
-    bool operator==(__sso_allocator& __a) const {return &buf_ == &__a.buf_;}
+    bool operator==(const __sso_allocator& __a) const {return &buf_ == &__a.buf_;}
     _LIBCPP_INLINE_VISIBILITY
-    bool operator!=(__sso_allocator& __a) const {return &buf_ != &__a.buf_;}
+    bool operator!=(const __sso_allocator& __a) const {return &buf_ != &__a.buf_;}
 };
 
 _LIBCPP_END_NAMESPACE_STD
 
-#endif // _LIBCPP___SSO_ALLOCATOR
+#endif // _LIBCPP_SSO_ALLOCATOR_H
diff --git a/libcxx/src/locale.cpp b/libcxx/src/locale.cpp
--- a/libcxx/src/locale.cpp
+++ b/libcxx/src/locale.cpp
@@ -27,7 +27,6 @@
 #define _CTYPE_DISABLE_MACROS
 #endif
 #include "cwctype"
-#include "__sso_allocator"
 #if defined(_LIBCPP_MSVCRT) || defined(__MINGW32__)
 #include "__support/win32/locale_win32.h"
 #elif !defined(__BIONIC__) && !defined(__NuttX__)
@@ -36,6 +35,7 @@
 #include <stdlib.h>
 #include <stdio.h>
 #include "include/atomic_support.h"
+#include "include/sso_allocator.h"
 #include "__undef_macros"
 
 // On Linux, wint_t and wchar_t have different signed-ness, and this causes