diff --git a/src/backend/utils/adt/formatting.c b/src/backend/utils/adt/formatting.c
index 3ef10dc..ef21b7e 100644
--- a/src/backend/utils/adt/formatting.c
+++ b/src/backend/utils/adt/formatting.c
@@ -1044,7 +1044,7 @@ static void parse_format(FormatNode *node, const char *str, const KeyWord *kw,
 
 static void DCH_to_char(FormatNode *node, bool is_interval,
 						TmToChar *in, char *out, Oid collid);
-static void DCH_from_char(FormatNode *node, char *in, TmFromChar *out,
+static void DCH_from_char(FormatNode *node, const char *in, TmFromChar *out,
 						  bool std, bool *have_error);
 
 #ifdef DEBUG_TO_FROM_CHAR
@@ -1055,17 +1055,17 @@ static void dump_node(FormatNode *node, int max);
 static const char *get_th(char *num, int type);
 static char *str_numth(char *dest, char *num, int type);
 static int	adjust_partial_year_to_2020(int year);
-static int	strspace_len(char *str);
+static int	strspace_len(const char *str);
 static void from_char_set_mode(TmFromChar *tmfc, const FromCharDateMode mode,
 							   bool *have_error);
 static void from_char_set_int(int *dest, const int value, const FormatNode *node,
 							  bool *have_error);
-static int	from_char_parse_int_len(int *dest, char **src, const int len,
+static int	from_char_parse_int_len(int *dest, const char **src, const int len,
 									FormatNode *node, bool *have_error);
-static int	from_char_parse_int(int *dest, char **src, FormatNode *node,
+static int	from_char_parse_int(int *dest, const char **src, FormatNode *node,
 								bool *have_error);
 static int	seq_search(const char *name, const char *const *array, int *len);
-static int	from_char_seq_search(int *dest, char **src,
+static int	from_char_seq_search(int *dest, const char **src,
 								 const char *const *array, int max,
 								 FormatNode *node, bool *have_error);
 static void do_to_timestamp(text *date_txt, text *fmt, bool std,
@@ -2255,7 +2255,7 @@ adjust_partial_year_to_2020(int year)
 
 
 static int
-strspace_len(char *str)
+strspace_len(const char *str)
 {
 	int			len = 0;
 
@@ -2344,12 +2344,12 @@ on_error:
  * and -1 is returned.
  */
 static int
-from_char_parse_int_len(int *dest, char **src, const int len, FormatNode *node,
+from_char_parse_int_len(int *dest, const char **src, const int len, FormatNode *node,
 						bool *have_error)
 {
 	long		result;
 	char		copy[DCH_MAX_ITEM_SIZ + 1];
-	char	   *init = *src;
+	const char *init = *src;
 	int			used;
 
 	/*
@@ -2366,8 +2366,11 @@ from_char_parse_int_len(int *dest, char **src, const int len, FormatNode *node,
 		 * This node is in Fill Mode, or the next node is known to be a
 		 * non-digit value, so we just slurp as many characters as we can get.
 		 */
+		char	   *endptr;
+
 		errno = 0;
-		result = strtol(init, src, 10);
+		result = strtol(init, &endptr, 10);
+		*src = endptr;
 	}
 	else
 	{
@@ -2444,7 +2447,7 @@ on_error:
  * required length explicitly.
  */
 static int
-from_char_parse_int(int *dest, char **src, FormatNode *node, bool *have_error)
+from_char_parse_int(int *dest, const char **src, FormatNode *node, bool *have_error)
 {
 	return from_char_parse_int_len(dest, src, node->key->len, node, have_error);
 }
@@ -2524,7 +2527,7 @@ seq_search(const char *name, const char *const *array, int *len)
  * node->key->name identifies what we were searching for.
  */
 static int
-from_char_seq_search(int *dest, char **src, const char *const *array,
+from_char_seq_search(int *dest, const char **src, const char *const *array,
 					 int max, FormatNode *node, bool *have_error)
 {
 	int			len;
@@ -3158,11 +3161,11 @@ DCH_to_char(FormatNode *node, bool is_interval, TmToChar *in, char *out, Oid col
  * ----------
  */
 static void
-DCH_from_char(FormatNode *node, char *in, TmFromChar *out, bool std,
+DCH_from_char(FormatNode *node, const char *in, TmFromChar *out, bool std,
 			  bool *have_error)
 {
 	FormatNode *n;
-	char	   *s;
+	const char *s;
 	int			len,
 				value;
 	bool		fx_mode = std;