diff --git a/build/cmake/setup.cmake b/build/cmake/setup.cmake
index 9e0e4d24d4..a21a2449a8 100644
--- a/build/cmake/setup.cmake
+++ b/build/cmake/setup.cmake
@@ -649,6 +649,7 @@ if(wxUSE_FSWATCHER)
 endif()
 
 if(wxUSE_XLOCALE)
+    check_include_file(xlocale.h HAVE_XLOCALE_H)
     set(CMAKE_EXTRA_INCLUDE_FILES xlocale.h locale.h)
     check_type_size(locale_t LOCALE_T)
     set(CMAKE_EXTRA_INCLUDE_FILES)
diff --git a/build/cmake/setup.h.in b/build/cmake/setup.h.in
index ab342723f1..4f244d7da4 100644
--- a/build/cmake/setup.h.in
+++ b/build/cmake/setup.h.in
@@ -1257,6 +1257,9 @@
 /* Define if setpriority() is available. */
 #cmakedefine HAVE_SETPRIORITY 1
 
+/* Define if xlocale.h header file exists. */
+#cmakedefine HAVE_XLOCALE_H 1
+
 /* Define if locale_t is available */
 #cmakedefine HAVE_LOCALE_T 1
 
diff --git a/configure b/configure
index 9c1e4bc12d..7266ef5019 100755
--- a/configure
+++ b/configure
@@ -3217,6 +3217,97 @@ fi
   as_fn_set_status $ac_retval
 
 } # ac_fn_cxx_try_run
+
+# ac_fn_c_check_header_mongrel LINENO HEADER VAR INCLUDES
+# -------------------------------------------------------
+# Tests whether HEADER exists, giving a warning if it cannot be compiled using
+# the include files in INCLUDES and setting the cache variable VAR
+# accordingly.
+ac_fn_c_check_header_mongrel ()
+{
+  as_lineno=${as_lineno-"$1"} as_lineno_stack=as_lineno_stack=$as_lineno_stack
+  if eval \${$3+:} false; then :
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for $2" >&5
+$as_echo_n "checking for $2... " >&6; }
+if eval \${$3+:} false; then :
+  $as_echo_n "(cached) " >&6
+fi
+eval ac_res=\$$3
+	       { $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_res" >&5
+$as_echo "$ac_res" >&6; }
+else
+  # Is the header compilable?
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking $2 usability" >&5
+$as_echo_n "checking $2 usability... " >&6; }
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+$4
+#include <$2>
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+  ac_header_compiler=yes
+else
+  ac_header_compiler=no
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_header_compiler" >&5
+$as_echo "$ac_header_compiler" >&6; }
+
+# Is the header present?
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking $2 presence" >&5
+$as_echo_n "checking $2 presence... " >&6; }
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+#include <$2>
+_ACEOF
+if ac_fn_c_try_cpp "$LINENO"; then :
+  ac_header_preproc=yes
+else
+  ac_header_preproc=no
+fi
+rm -f conftest.err conftest.i conftest.$ac_ext
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_header_preproc" >&5
+$as_echo "$ac_header_preproc" >&6; }
+
+# So?  What about this header?
+case $ac_header_compiler:$ac_header_preproc:$ac_c_preproc_warn_flag in #((
+  yes:no: )
+    { $as_echo "$as_me:${as_lineno-$LINENO}: WARNING: $2: accepted by the compiler, rejected by the preprocessor!" >&5
+$as_echo "$as_me: WARNING: $2: accepted by the compiler, rejected by the preprocessor!" >&2;}
+    { $as_echo "$as_me:${as_lineno-$LINENO}: WARNING: $2: proceeding with the compiler's result" >&5
+$as_echo "$as_me: WARNING: $2: proceeding with the compiler's result" >&2;}
+    ;;
+  no:yes:* )
+    { $as_echo "$as_me:${as_lineno-$LINENO}: WARNING: $2: present but cannot be compiled" >&5
+$as_echo "$as_me: WARNING: $2: present but cannot be compiled" >&2;}
+    { $as_echo "$as_me:${as_lineno-$LINENO}: WARNING: $2:     check for missing prerequisite headers?" >&5
+$as_echo "$as_me: WARNING: $2:     check for missing prerequisite headers?" >&2;}
+    { $as_echo "$as_me:${as_lineno-$LINENO}: WARNING: $2: see the Autoconf documentation" >&5
+$as_echo "$as_me: WARNING: $2: see the Autoconf documentation" >&2;}
+    { $as_echo "$as_me:${as_lineno-$LINENO}: WARNING: $2:     section \"Present But Cannot Be Compiled\"" >&5
+$as_echo "$as_me: WARNING: $2:     section \"Present But Cannot Be Compiled\"" >&2;}
+    { $as_echo "$as_me:${as_lineno-$LINENO}: WARNING: $2: proceeding with the compiler's result" >&5
+$as_echo "$as_me: WARNING: $2: proceeding with the compiler's result" >&2;}
+( $as_echo "## -------------------------------------- ##
+## Report this to wx-dev@googlegroups.com ##
+## -------------------------------------- ##"
+     ) | sed "s/^/$as_me: WARNING:     /" >&2
+    ;;
+esac
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for $2" >&5
+$as_echo_n "checking for $2... " >&6; }
+if eval \${$3+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  eval "$3=\$ac_header_compiler"
+fi
+eval ac_res=\$$3
+	       { $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_res" >&5
+$as_echo "$ac_res" >&6; }
+fi
+  eval $as_lineno_stack; ${as_lineno_stack:+:} unset as_lineno
+
+} # ac_fn_c_check_header_mongrel
 cat >config.log <<_ACEOF
 This file contains any messages produced by compilers while
 running configure, to aid debugging if configure makes a mistake.
@@ -32907,6 +32998,19 @@ $as_echo "$as_me: WARNING: I18n code requires wxFile... disabled" >&2;}
 fi
 
 if test "$wxUSE_XLOCALE" = "yes" ; then
+            for ac_header in xlocale.h
+do :
+  ac_fn_c_check_header_mongrel "$LINENO" "xlocale.h" "ac_cv_header_xlocale_h" "$ac_includes_default"
+if test "x$ac_cv_header_xlocale_h" = xyes; then :
+  cat >>confdefs.h <<_ACEOF
+#define HAVE_XLOCALE_H 1
+_ACEOF
+
+fi
+
+done
+
+
     { $as_echo "$as_me:${as_lineno-$LINENO}: checking for locale_t" >&5
 $as_echo_n "checking for locale_t... " >&6; }
 if ${wx_cv_type_locale_t+:} false; then :
@@ -32922,6 +33026,9 @@ ac_compiler_gnu=$ac_cv_cxx_compiler_gnu
         cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
+        #ifdef HAVE_XLOCALE_H
+        #include <xlocale.h>
+        #endif
         #include <locale.h>
         #include <stdlib.h>
 
diff --git a/configure.in b/configure.in
index c9a84bb3a6..5af395548d 100644
--- a/configure.in
+++ b/configure.in
@@ -5757,11 +5757,18 @@ if test "$wxUSE_INTL" = "yes" ; then
 fi
 
 if test "$wxUSE_XLOCALE" = "yes" ; then
+    dnl Some platforms (e.g. macOS) require an extra header, others (Linux)
+    dnl don't, but it's simpler to just check for it under all of them.
+    AC_CHECK_HEADERS([xlocale.h])
+
     AC_CACHE_CHECK([for locale_t], wx_cv_type_locale_t,
     [
         AC_LANG_PUSH(C++)
         AC_TRY_COMPILE(
         [
+        #ifdef HAVE_XLOCALE_H
+        #include <xlocale.h>
+        #endif
         #include <locale.h>
         #include <stdlib.h>
         ],
diff --git a/include/wx/xlocale.h b/include/wx/xlocale.h
index 9ade3a99f4..476a3a737e 100644
--- a/include/wx/xlocale.h
+++ b/include/wx/xlocale.h
@@ -40,6 +40,11 @@
         typedef _locale_t wxXLocale_t;
         #define wxXLOCALE_IDENT(name) _ ## name
     #elif defined(HAVE_LOCALE_T)
+        // Some systems (notably macOS) require including a separate header for
+        // locale_t and related functions.
+        #ifdef HAVE_XLOCALE_H
+            #include <xlocale.h>
+        #endif
         #include <locale.h>
         #include <ctype.h>
         #include <stdlib.h>
diff --git a/setup.h.in b/setup.h.in
index 1f1955ad4c..981b45e1da 100644
--- a/setup.h.in
+++ b/setup.h.in
@@ -1267,6 +1267,9 @@
 /* Define if setpriority() is available. */
 #undef HAVE_SETPRIORITY
 
+/* Define if xlocale.h header file exists. */
+#undef HAVE_XLOCALE_H
+
 /* Define if locale_t is available */
 #undef HAVE_LOCALE_T