diff --git a/src/backend/commands/dbcommands.c b/src/backend/commands/dbcommands.c
index 5fbbcdaabb1d..006514fb160f 100644
--- a/src/backend/commands/dbcommands.c
+++ b/src/backend/commands/dbcommands.c
@@ -730,7 +730,6 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 	const char *dblocale = NULL;
 	char	   *dbicurules = NULL;
 	char		dblocprovider = '\0';
-	char	   *canonname;
 	int			encoding = -1;
 	bool		dbistemplate = false;
 	bool		dballowconnections = true;
@@ -1064,18 +1063,16 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 				 errmsg("invalid server encoding %d", encoding)));
 
 	/* Check that the chosen locales are valid, and get canonical spellings */
-	if (!check_locale(LC_COLLATE, dbcollate, &canonname))
+	if (!check_locale(LC_COLLATE, dbcollate))
 		ereport(ERROR,
 				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
 				 errmsg("invalid LC_COLLATE locale name: \"%s\"", dbcollate),
 				 errhint("If the locale name is specific to ICU, use ICU_LOCALE.")));
-	dbcollate = canonname;
-	if (!check_locale(LC_CTYPE, dbctype, &canonname))
+	if (!check_locale(LC_CTYPE, dbctype))
 		ereport(ERROR,
 				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
 				 errmsg("invalid LC_CTYPE locale name: \"%s\"", dbctype),
 				 errhint("If the locale name is specific to ICU, use ICU_LOCALE.")));
-	dbctype = canonname;
 
 	check_encoding_locale_matches(encoding, dbcollate, dbctype);
 
diff --git a/src/backend/utils/adt/pg_locale.c b/src/backend/utils/adt/pg_locale.c
index 6e43b708c0f7..44621acf9c92 100644
--- a/src/backend/utils/adt/pg_locale.c
+++ b/src/backend/utils/adt/pg_locale.c
@@ -172,6 +172,36 @@ static pg_locale_t last_collation_cache_locale = NULL;
 static char *IsoLocaleName(const char *);
 #endif
 
+#ifndef WIN32
+/*
+ * The newlocale() function needs LC_xxx_MASK, but sometimes we have LC_xxx,
+ * and POSIX doesn't offer a way to translate.
+ */
+static int
+get_lc_category_mask(int category)
+{
+	switch (category)
+	{
+		case LC_COLLATE:
+			return LC_COLLATE_MASK;
+		case LC_CTYPE:
+			return LC_CTYPE_MASK;
+#ifdef LC_MESSAGES
+		case LC_MESSAGES:
+			return LC_MESSAGES_MASK;
+#endif
+		case LC_MONETARY:
+			return LC_MONETARY_MASK;
+		case LC_NUMERIC:
+			return LC_NUMERIC_MASK;
+		case LC_TIME:
+			return LC_TIME_MASK;
+		default:
+			return 0;
+	};
+}
+#endif
+
 /*
  * pg_perm_setlocale
  *
@@ -281,19 +311,11 @@ pg_perm_setlocale(int category, const char *locale)
 
 /*
  * Is the locale name valid for the locale category?
- *
- * If successful, and canonname isn't NULL, a palloc'd copy of the locale's
- * canonical name is stored there.  This is especially useful for figuring out
- * what locale name "" means (ie, the server environment value).  (Actually,
- * it seems that on most implementations that's the only thing it's good for;
- * we could wish that setlocale gave back a canonically spelled version of
- * the locale name, but typically it doesn't.)
  */
 bool
-check_locale(int category, const char *locale, char **canonname)
+check_locale(int category, const char *locale)
 {
-	char	   *save;
-	char	   *res;
+	locale_t	loc;
 
 	/* Don't let Windows' non-ASCII locale names in. */
 	if (!pg_is_ascii(locale))
@@ -305,41 +327,42 @@ check_locale(int category, const char *locale, char **canonname)
 		return false;
 	}
 
-	if (canonname)
-		*canonname = NULL;		/* in case of failure */
-
-	save = setlocale(category, NULL);
-	if (!save)
-		return false;			/* won't happen, we hope */
-
-	/* save may be pointing at a modifiable scratch variable, see above. */
-	save = pstrdup(save);
-
-	/* set the locale with setlocale, to see if it accepts it. */
-	res = setlocale(category, locale);
-
-	/* save canonical name if requested. */
-	if (res && canonname)
-		*canonname = pstrdup(res);
-
-	/* restore old value. */
-	if (!setlocale(category, save))
-		elog(WARNING, "failed to restore old locale \"%s\"", save);
-	pfree(save);
+	if (locale[0] == 0)
+	{
+		/*
+		 * We only accept explicit locale names, not "".  We don't want to
+		 * rely on environment variables in the backend.
+		 */
+		return false;
+	}
 
-	/* Don't let Windows' non-ASCII locale names out. */
-	if (canonname && *canonname && !pg_is_ascii(*canonname))
+	/*
+	 * See if we can open it.  Unfortunately we can't always distinguish
+	 * out-of-memory from invalid locale name.
+	 */
+	errno = ENOENT;
+#ifdef WIN32
+	loc = _create_locale(category, locale);
+	if (loc == (locale_t) 0)
+		_dosmaperr(GetLastError());
+#else
+	loc = newlocale(get_lc_category_mask(category), locale, (locale_t) 0);
+#endif
+	if (loc == (locale_t) 0)
 	{
-		ereport(WARNING,
-				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-				 errmsg("locale name \"%s\" contains non-ASCII characters",
-						*canonname)));
-		pfree(*canonname);
-		*canonname = NULL;
+		if (errno == ENOMEM)
+			elog(ERROR, "out of memory");
+
+		/* Otherwise assume the locale doesn't exist. */
 		return false;
 	}
+#ifdef WIN32
+	_free_locale(loc);
+#else
+	freelocale(loc);
+#endif
 
-	return (res != NULL);
+	return true;
 }
 
 
@@ -357,7 +380,7 @@ check_locale(int category, const char *locale, char **canonname)
 bool
 check_locale_monetary(char **newval, void **extra, GucSource source)
 {
-	return check_locale(LC_MONETARY, *newval, NULL);
+	return check_locale(LC_MONETARY, *newval);
 }
 
 void
@@ -369,7 +392,7 @@ assign_locale_monetary(const char *newval, void *extra)
 bool
 check_locale_numeric(char **newval, void **extra, GucSource source)
 {
-	return check_locale(LC_NUMERIC, *newval, NULL);
+	return check_locale(LC_NUMERIC, *newval);
 }
 
 void
@@ -381,7 +404,7 @@ assign_locale_numeric(const char *newval, void *extra)
 bool
 check_locale_time(char **newval, void **extra, GucSource source)
 {
-	return check_locale(LC_TIME, *newval, NULL);
+	return check_locale(LC_TIME, *newval);
 }
 
 void
@@ -417,7 +440,7 @@ check_locale_messages(char **newval, void **extra, GucSource source)
 	 * On Windows, we can't even check the value, so accept blindly
 	 */
 #if defined(LC_MESSAGES) && !defined(WIN32)
-	return check_locale(LC_MESSAGES, *newval, NULL);
+	return check_locale(LC_MESSAGES, *newval);
 #else
 	return true;
 #endif
diff --git a/src/bin/initdb/initdb.c b/src/bin/initdb/initdb.c
index c17fda2bc81d..464788612e06 100644
--- a/src/bin/initdb/initdb.c
+++ b/src/bin/initdb/initdb.c
@@ -2203,8 +2203,6 @@ locale_date_order(const char *locale)
  * it seems that on most implementations that's the only thing it's good for;
  * we could wish that setlocale gave back a canonically spelled version of
  * the locale name, but typically it doesn't.)
- *
- * this should match the backend's check_locale() function
  */
 static void
 check_locale_name(int category, const char *locale, char **canonname)
diff --git a/src/include/utils/pg_locale.h b/src/include/utils/pg_locale.h
index 7df90f43f60e..32a41913c3fe 100644
--- a/src/include/utils/pg_locale.h
+++ b/src/include/utils/pg_locale.h
@@ -35,7 +35,7 @@ extern PGDLLIMPORT char *localized_full_months[];
 /* is the databases's LC_CTYPE the C locale? */
 extern PGDLLIMPORT bool database_ctype_is_c;
 
-extern bool check_locale(int category, const char *locale, char **canonname);
+extern bool check_locale(int category, const char *locale);
 extern char *pg_perm_setlocale(int category, const char *locale);
 
 /*
diff --git a/src/port/chklocale.c b/src/port/chklocale.c
index 034939f7fd2c..d622c09e9bb5 100644
--- a/src/port/chklocale.c
+++ b/src/port/chklocale.c
@@ -183,6 +183,7 @@ static const struct encoding_match encoding_match_list[] = {
 	{PG_SHIFT_JIS_2004, "SJIS_2004"},
 
 	{PG_SQL_ASCII, "US-ASCII"},
+	{PG_SQL_ASCII, "646"},
 
 	{PG_SQL_ASCII, NULL}		/* end marker */
 };