diff --git a/src/backend/utils/adt/formatting.c b/src/backend/utils/adt/formatting.c
index 5b210ebeaeb..71980899cc3 100644
--- a/src/backend/utils/adt/formatting.c
+++ b/src/backend/utils/adt/formatting.c
@@ -1644,6 +1644,87 @@ str_initcap(const char *buff, size_t nbytes)
 	return result;
 }
 
+/*
+ * ASCII-only lower function
+ *
+ * We pass the number of bytes so we can pass varlena and char*
+ * to this function.  The result is a palloc'd, null-terminated string.
+ */
+char *
+asc_tolower(const char *buff, size_t nbytes)
+{
+	char	   *result;
+	char	   *p;
+
+	if (!buff)
+		return NULL;
+
+	result = pnstrdup(buff, nbytes);
+
+	for (p = result; *p; p++)
+		*p = pg_tolower((unsigned char) *p);
+
+	return result;
+}
+
+/*
+ * ASCII-only upper function
+ *
+ * We pass the number of bytes so we can pass varlena and char*
+ * to this function.  The result is a palloc'd, null-terminated string.
+ */
+char *
+asc_toupper(const char *buff, size_t nbytes)
+{
+	char	   *result;
+	char	   *p;
+
+	if (!buff)
+		return NULL;
+
+	result = pnstrdup(buff, nbytes);
+
+	for (p = result; *p; p++)
+		*p = pg_toupper((unsigned char) *p);
+
+	return result;
+}
+
+/*
+ * ASCII-only initcap function
+ *
+ * We pass the number of bytes so we can pass varlena and char*
+ * to this function.  The result is a palloc'd, null-terminated string.
+ */
+char *
+asc_initcap(const char *buff, size_t nbytes)
+{
+	char	   *result;
+	char	   *p;
+	int			wasalnum = false;
+
+	if (!buff)
+		return NULL;
+
+	result = pnstrdup(buff, nbytes);
+
+	for (p = result; *p; p++)
+	{
+		char		c;
+
+		if (wasalnum)
+			*p = c = pg_tolower((unsigned char) *p);
+		else
+			*p = c = pg_toupper((unsigned char) *p);
+		/* we don't trust isalnum() here */
+		wasalnum = ((c >= 'A' && c <= 'Z') ||
+					(c >= 'a' && c <= 'z') ||
+					(c >= '0' && c <= '9'));
+	}
+
+	return result;
+}
+
 /* convenience routines for when the input is null-terminated */
 
 static char *
@@ -1664,6 +1745,20 @@ str_initcap_z(const char *buff)
 	return str_initcap(buff, strlen(buff));
 }
 
+static char *
+asc_tolower_z(const char *buff)
+{
+	return asc_tolower(buff, strlen(buff));
+}
+
+static char *
+asc_toupper_z(const char *buff)
+{
+	return asc_toupper(buff, strlen(buff));
+}
+
+/* asc_initcap_z is not currently needed */
+
 
 /* ----------
  * Skip TM / th in FROM_CHAR
@@ -2151,7 +2246,8 @@ DCH_to_char(FormatNode *node, bool is_interval, TmToChar *in, char *out)
 				INVALID_FOR_INTERVAL;
 				if (tmtcTzn(in))
 				{
-					char	   *p = str_tolower_z(tmtcTzn(in));
+					/* We assume here that timezone names aren't localized */
+					char	   *p = asc_tolower_z(tmtcTzn(in));
 
 					strcpy(s, p);
 					pfree(p);
@@ -2198,7 +2294,7 @@ DCH_to_char(FormatNode *node, bool is_interval, TmToChar *in, char *out)
 					strcpy(s, str_toupper_z(localized_full_months[tm->tm_mon - 1]));
 				else
 					sprintf(s, "%*s", S_FM(n->suffix) ? 0 : -9,
-							str_toupper_z(months_full[tm->tm_mon - 1]));
+							asc_toupper_z(months_full[tm->tm_mon - 1]));
 				s += strlen(s);
 				break;
 			case DCH_Month:
@@ -2208,7 +2304,8 @@ DCH_to_char(FormatNode *node, bool is_interval, TmToChar *in, char *out)
 				if (S_TM(n->suffix))
 					strcpy(s, str_initcap_z(localized_full_months[tm->tm_mon - 1]));
 				else
-					sprintf(s, "%*s", S_FM(n->suffix) ? 0 : -9, months_full[tm->tm_mon - 1]);
+					sprintf(s, "%*s", S_FM(n->suffix) ? 0 : -9,
+							months_full[tm->tm_mon - 1]);
 				s += strlen(s);
 				break;
 			case DCH_month:
@@ -2218,10 +2315,8 @@ DCH_to_char(FormatNode *node, bool is_interval, TmToChar *in, char *out)
 				if (S_TM(n->suffix))
 					strcpy(s, str_tolower_z(localized_full_months[tm->tm_mon - 1]));
 				else
-				{
-					sprintf(s, "%*s", S_FM(n->suffix) ? 0 : -9, months_full[tm->tm_mon - 1]);
-					*s = pg_tolower((unsigned char) *s);
-				}
+					sprintf(s, "%*s", S_FM(n->suffix) ? 0 : -9,
+							asc_tolower_z(months_full[tm->tm_mon - 1]));
 				s += strlen(s);
 				break;
 			case DCH_MON:
@@ -2231,7 +2326,7 @@ DCH_to_char(FormatNode *node, bool is_interval, TmToChar *in, char *out)
 				if (S_TM(n->suffix))
 					strcpy(s, str_toupper_z(localized_abbrev_months[tm->tm_mon - 1]));
 				else
-					strcpy(s, str_toupper_z(months[tm->tm_mon - 1]));
+					strcpy(s, asc_toupper_z(months[tm->tm_mon - 1]));
 				s += strlen(s);
 				break;
 			case DCH_Mon:
@@ -2251,10 +2346,7 @@ DCH_to_char(FormatNode *node, bool is_interval, TmToChar *in, char *out)
 				if (S_TM(n->suffix))
 					strcpy(s, str_tolower_z(localized_abbrev_months[tm->tm_mon - 1]));
 				else
-				{
-					strcpy(s, months[tm->tm_mon - 1]);
-					*s = pg_tolower((unsigned char) *s);
-				}
+					strcpy(s, asc_tolower_z(months[tm->tm_mon - 1]));
 				s += strlen(s);
 				break;
 			case DCH_MM:
@@ -2269,7 +2361,7 @@ DCH_to_char(FormatNode *node, bool is_interval, TmToChar *in, char *out)
 					strcpy(s, str_toupper_z(localized_full_days[tm->tm_wday]));
 				else
 					sprintf(s, "%*s", S_FM(n->suffix) ? 0 : -9,
-							str_toupper_z(days[tm->tm_wday]));
+							asc_toupper_z(days[tm->tm_wday]));
 				s += strlen(s);
 				break;
 			case DCH_Day:
@@ -2277,7 +2369,8 @@ DCH_to_char(FormatNode *node, bool is_interval, TmToChar *in, char *out)
 				if (S_TM(n->suffix))
 					strcpy(s, str_initcap_z(localized_full_days[tm->tm_wday]));
 				else
-					sprintf(s, "%*s", S_FM(n->suffix) ? 0 : -9, days[tm->tm_wday]);
+					sprintf(s, "%*s", S_FM(n->suffix) ? 0 : -9,
+							days[tm->tm_wday]);
 				s += strlen(s);
 				break;
 			case DCH_day:
@@ -2285,10 +2378,8 @@ DCH_to_char(FormatNode *node, bool is_interval, TmToChar *in, char *out)
 				if (S_TM(n->suffix))
 					strcpy(s, str_tolower_z(localized_full_days[tm->tm_wday]));
 				else
-				{
-					sprintf(s, "%*s", S_FM(n->suffix) ? 0 : -9, days[tm->tm_wday]);
-					*s = pg_tolower((unsigned char) *s);
-				}
+					sprintf(s, "%*s", S_FM(n->suffix) ? 0 : -9,
+							asc_tolower_z(days[tm->tm_wday]));
 				s += strlen(s);
 				break;
 			case DCH_DY:
@@ -2296,7 +2387,7 @@ DCH_to_char(FormatNode *node, bool is_interval, TmToChar *in, char *out)
 				if (S_TM(n->suffix))
 					strcpy(s, str_toupper_z(localized_abbrev_days[tm->tm_wday]));
 				else
-					strcpy(s, str_toupper_z(days_short[tm->tm_wday]));
+					strcpy(s, asc_toupper_z(days_short[tm->tm_wday]));
 				s += strlen(s);
 				break;
 			case DCH_Dy:
@@ -2312,10 +2403,7 @@ DCH_to_char(FormatNode *node, bool is_interval, TmToChar *in, char *out)
 				if (S_TM(n->suffix))
 					strcpy(s, str_tolower_z(localized_abbrev_days[tm->tm_wday]));
 				else
-				{
-					strcpy(s, days_short[tm->tm_wday]);
-					*s = pg_tolower((unsigned char) *s);
-				}
+					strcpy(s, asc_tolower_z(days_short[tm->tm_wday]));
 				s += strlen(s);
 				break;
 			case DCH_DDD:
@@ -4422,12 +4510,12 @@ NUM_processor(FormatNode *node, NUMDesc *Num, char *inout, char *number,
 				case NUM_rn:
 					if (IS_FILLMODE(Np->Num))
 					{
-						strcpy(Np->inout_p, str_tolower_z(Np->number_p));
+						strcpy(Np->inout_p, asc_tolower_z(Np->number_p));
 						Np->inout_p += strlen(Np->inout_p) - 1;
 					}
 					else
 					{
-						sprintf(Np->inout_p, "%15s", str_tolower_z(Np->number_p));
+						sprintf(Np->inout_p, "%15s", asc_tolower_z(Np->number_p));
 						Np->inout_p += strlen(Np->inout_p) - 1;
 					}
 					break;
diff --git a/src/include/utils/formatting.h b/src/include/utils/formatting.h
index da206b6fb86..714d641623d 100644
--- a/src/include/utils/formatting.h
+++ b/src/include/utils/formatting.h
@@ -25,6 +25,10 @@ extern char *str_tolower(const char *buff, size_t nbytes);
 extern char *str_toupper(const char *buff, size_t nbytes);
 extern char *str_initcap(const char *buff, size_t nbytes);
 
+extern char *asc_tolower(const char *buff, size_t nbytes);
+extern char *asc_toupper(const char *buff, size_t nbytes);
+extern char *asc_initcap(const char *buff, size_t nbytes);
+
 extern Datum timestamp_to_char(PG_FUNCTION_ARGS);
 extern Datum timestamptz_to_char(PG_FUNCTION_ARGS);
 extern Datum interval_to_char(PG_FUNCTION_ARGS);