diff --git a/src/backend/utils/adt/formatting.c b/src/backend/utils/adt/formatting.c
index 1d05481181db..c80e44617e36 100644
--- a/src/backend/utils/adt/formatting.c
+++ b/src/backend/utils/adt/formatting.c
@@ -1565,6 +1565,11 @@ get_th(char *num, int type)
 	int			len = strlen(num),
 				last;
 
+	if (len == 0)
+		ereport(ERROR,
+				(errcode(ERRCODE_ZERO_LENGTH_CHARACTER_STRING),
+				 errmsg("input cannot be empty string")));
+
 	last = *(num + (len - 1));
 	if (!isdigit((unsigned char) last))
 		ereport(ERROR,