diff --git a/src/backend/nodes/readfuncs.c b/src/backend/nodes/readfuncs.c
index dcec3b728f2..76cff8a2b15 100644
--- a/src/backend/nodes/readfuncs.c
+++ b/src/backend/nodes/readfuncs.c
@@ -80,7 +80,7 @@
 #define READ_UINT64_FIELD(fldname) \
 	token = pg_strtok(&length);		/* skip :fldname */ \
 	token = pg_strtok(&length);		/* get field value */ \
-	local_node->fldname = pg_strtouint64(token, NULL, 10)
+	local_node->fldname = strtou64(token, NULL, 10)
 
 /* Read a long integer field (anything written as ":fldname %ld") */
 #define READ_LONG_FIELD(fldname) \
diff --git a/src/backend/utils/adt/numutils.c b/src/backend/utils/adt/numutils.c
index b93096f288f..6a9c00fdd3e 100644
--- a/src/backend/utils/adt/numutils.c
+++ b/src/backend/utils/adt/numutils.c
@@ -606,25 +606,3 @@ pg_ultostr(char *str, uint32 value)
 
 	return str + len;
 }
-
-/*
- * pg_strtouint64
- *		Converts 'str' into an unsigned 64-bit integer.
- *
- * This has the identical API to strtoul(3), except that it will handle
- * 64-bit ints even where "long" is narrower than that.
- *
- * For the moment it seems sufficient to assume that the platform has
- * such a function somewhere; let's not roll our own.
- */
-uint64
-pg_strtouint64(const char *str, char **endptr, int base)
-{
-#ifdef _MSC_VER					/* MSVC only */
-	return _strtoui64(str, endptr, base);
-#elif defined(HAVE_STRTOULL) && SIZEOF_LONG < 8
-	return strtoull(str, endptr, base);
-#else
-	return strtoul(str, endptr, base);
-#endif
-}
diff --git a/src/backend/utils/adt/xid.c b/src/backend/utils/adt/xid.c
index 24c1c937326..a09096d0187 100644
--- a/src/backend/utils/adt/xid.c
+++ b/src/backend/utils/adt/xid.c
@@ -158,7 +158,7 @@ xid8in(PG_FUNCTION_ARGS)
 {
 	char	   *str = PG_GETARG_CSTRING(0);
 
-	PG_RETURN_FULLTRANSACTIONID(FullTransactionIdFromU64(pg_strtouint64(str, NULL, 0)));
+	PG_RETURN_FULLTRANSACTIONID(FullTransactionIdFromU64(strtou64(str, NULL, 0)));
 }
 
 Datum
diff --git a/src/backend/utils/adt/xid8funcs.c b/src/backend/utils/adt/xid8funcs.c
index f1870a73668..68985dca5a6 100644
--- a/src/backend/utils/adt/xid8funcs.c
+++ b/src/backend/utils/adt/xid8funcs.c
@@ -295,12 +295,12 @@ parse_snapshot(const char *str)
 	char	   *endp;
 	StringInfo	buf;
 
-	xmin = FullTransactionIdFromU64(pg_strtouint64(str, &endp, 10));
+	xmin = FullTransactionIdFromU64(strtou64(str, &endp, 10));
 	if (*endp != ':')
 		goto bad_format;
 	str = endp + 1;
 
-	xmax = FullTransactionIdFromU64(pg_strtouint64(str, &endp, 10));
+	xmax = FullTransactionIdFromU64(strtou64(str, &endp, 10));
 	if (*endp != ':')
 		goto bad_format;
 	str = endp + 1;
@@ -318,7 +318,7 @@ parse_snapshot(const char *str)
 	while (*str != '\0')
 	{
 		/* read next value */
-		val = FullTransactionIdFromU64(pg_strtouint64(str, &endp, 10));
+		val = FullTransactionIdFromU64(strtou64(str, &endp, 10));
 		str = endp;
 
 		/* require the input to be in order */
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index f736e8d8725..7b030463013 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -12438,7 +12438,7 @@ check_recovery_target_xid(char **newval, void **extra, GucSource source)
 		TransactionId *myextra;
 
 		errno = 0;
-		xid = (TransactionId) pg_strtouint64(*newval, NULL, 0);
+		xid = (TransactionId) strtou64(*newval, NULL, 0);
 		if (errno == EINVAL || errno == ERANGE)
 			return false;
 
diff --git a/src/include/c.h b/src/include/c.h
index 7e591171a84..98c0b053c98 100644
--- a/src/include/c.h
+++ b/src/include/c.h
@@ -1312,6 +1312,19 @@ extern long long strtoll(const char *str, char **endptr, int base);
 extern unsigned long long strtoull(const char *str, char **endptr, int base);
 #endif
 
+/*
+ * Thin wrappers that convert strings to exactly 64-bit integers, matching our
+ * definition of int64.  (For the naming, compare that POSIX has
+ * strtoimax()/strtoumax() which return intmax_t/uintmax_t.)
+ */
+#ifdef HAVE_LONG_INT_64
+#define strtoi64(str, endptr, base) ((int64) strtol(str, endptr, base))
+#define strtou64(str, endptr, base) ((uint64) strtoul(str, endptr, base))
+#else
+#define strtoi64(str, endptr, base) ((int64) strtoll(str, endptr, base))
+#define strtou64(str, endptr, base) ((uint64) strtoull(str, endptr, base))
+#endif
+
 /*
  * Use "extern PGDLLIMPORT ..." to declare variables that are defined
  * in the core backend and need to be accessible by loadable modules.
diff --git a/src/include/utils/builtins.h b/src/include/utils/builtins.h
index 40fcb0ab6d7..b07eefaf1ed 100644
--- a/src/include/utils/builtins.h
+++ b/src/include/utils/builtins.h
@@ -53,7 +53,6 @@ extern int	pg_ltoa(int32 l, char *a);
 extern int	pg_lltoa(int64 ll, char *a);
 extern char *pg_ultostr_zeropad(char *str, uint32 value, int32 minwidth);
 extern char *pg_ultostr(char *str, uint32 value);
-extern uint64 pg_strtouint64(const char *str, char **endptr, int base);
 
 /* oid.c */
 extern oidvector *buildoidvector(const Oid *oids, int n);