diff --git a/contrib/citext/citext--1.8--1.9.sql b/contrib/citext/citext--1.8--1.9.sql
index 6573f55b5f9..aa02961618f 100644
--- a/contrib/citext/citext--1.8--1.9.sql
+++ b/contrib/citext/citext--1.8--1.9.sql
@@ -3,18 +3,20 @@
 -- complain if script is sourced in psql, rather than via ALTER EXTENSION
 \echo Use "ALTER EXTENSION citext UPDATE TO '1.9'" to load this file. \quit
 
--- Follow the core split_part(): a negative position counts from the end, a
--- position past the last field returns an empty string, and a position of
--- zero is an error.  A zero position and an empty delimiter, where there is no
--- case to ignore, are left to the core function.
+-- Normalize the case of the delimiter occurrences in the string, and let the
+-- core split_part() do the splitting.  The fields themselves are not touched,
+-- so they keep their original case, while the field positions, the empty
+-- delimiter and the zero-position error all behave exactly as in core.
+-- The delimiter is escaped twice: once as a regular expression to search for,
+-- and once as a replacement string, where a backslash is also special.
 CREATE OR REPLACE FUNCTION split_part( citext, citext, int ) RETURNS TEXT
 LANGUAGE SQL IMMUTABLE STRICT PARALLEL SAFE
-RETURN CASE
-  WHEN $3 = 0 OR pg_catalog.length($2::pg_catalog.text) = 0 THEN
-    pg_catalog.split_part($1::pg_catalog.text, $2::pg_catalog.text, $3)
-  ELSE
-    (SELECT COALESCE(fields[CASE WHEN $3 > 0 THEN $3
-                                 ELSE pg_catalog.array_length(fields, 1) + $3 + 1 END],
-                     '')
-     FROM (SELECT pg_catalog.regexp_split_to_array( $1::pg_catalog.text, pg_catalog.regexp_replace($2::pg_catalog.text, '([^a-zA-Z_0-9])', E'\\\\\\1', 'g'), 'i') AS fields) AS s)
-END;
+RETURN pg_catalog.split_part(
+         pg_catalog.regexp_replace(
+           $1::pg_catalog.text,
+           pg_catalog.regexp_replace($2::pg_catalog.text,
+                                     '([^a-zA-Z_0-9])', E'\\\\\\1', 'g'),
+           pg_catalog.replace($2::pg_catalog.text, E'\\', E'\\\\'),
+           'gi'),
+         $2::pg_catalog.text,
+         $3);