diff --git a/src/backend/parser/parse_func.c b/src/backend/parser/parse_func.c
index 6717ddc6881..860767a52ee 100644
--- a/src/backend/parser/parse_func.c
+++ b/src/backend/parser/parse_func.c
@@ -359,7 +359,7 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 	if (fdresult != FUNCDETAIL_WINDOWFUNC && ignore_nulls != NO_NULLTREATMENT)
 		ereport(ERROR,
 				errcode(ERRCODE_WRONG_OBJECT_TYPE),
-				errmsg("Only window functions accept RESPECT/IGNORE NULLS"),
+				errmsg("only window functions accept RESPECT/IGNORE NULLS"),
 				parser_errposition(pstate, location));
 
 	/*
diff --git a/src/test/regress/expected/window.out b/src/test/regress/expected/window.out
index 891b0153004..59c3df8cf0a 100644
--- a/src/test/regress/expected/window.out
+++ b/src/test/regress/expected/window.out
@@ -5764,11 +5764,11 @@ SELECT sum(orbit) OVER () FROM planets; -- succeeds
 (10 rows)
 
 SELECT sum(orbit) RESPECT NULLS OVER () FROM planets; -- fails
-ERROR:  Only window functions accept RESPECT/IGNORE NULLS
+ERROR:  only window functions accept RESPECT/IGNORE NULLS
 LINE 1: SELECT sum(orbit) RESPECT NULLS OVER () FROM planets;
                ^
 SELECT sum(orbit) IGNORE NULLS OVER () FROM planets; -- fails
-ERROR:  Only window functions accept RESPECT/IGNORE NULLS
+ERROR:  only window functions accept RESPECT/IGNORE NULLS
 LINE 1: SELECT sum(orbit) IGNORE NULLS OVER () FROM planets;
                ^
 SELECT row_number() OVER () FROM planets; -- succeeds