diff --git a/src/backend/parser/parse_func.c b/src/backend/parser/parse_func.c
index 2e4cc1de50d..6717ddc6881 100644
--- a/src/backend/parser/parse_func.c
+++ b/src/backend/parser/parse_func.c
@@ -353,6 +353,15 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 					 parser_errposition(pstate, location)));
 	}
 
+	/*
+	 * NULL TREATEMENT is only allowed for window functions per spec.
+	 */
+	if (fdresult != FUNCDETAIL_WINDOWFUNC && ignore_nulls != NO_NULLTREATMENT)
+		ereport(ERROR,
+				errcode(ERRCODE_WRONG_OBJECT_TYPE),
+				errmsg("Only window functions accept RESPECT/IGNORE NULLS"),
+				parser_errposition(pstate, location));
+
 	/*
 	 * So far so good, so do some fdresult-type-specific processing.
 	 */
@@ -519,13 +528,6 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 						 errmsg("%s is not an ordered-set aggregate, so it cannot have WITHIN GROUP",
 								NameListToString(funcname)),
 						 parser_errposition(pstate, location)));
-
-			/* It also can't treat nulls as a window function */
-			if (ignore_nulls != NO_NULLTREATMENT)
-				ereport(ERROR,
-						(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-						 errmsg("aggregate functions do not accept RESPECT/IGNORE NULLS"),
-						 parser_errposition(pstate, location)));
 		}
 	}
 	else if (fdresult == FUNCDETAIL_WINDOWFUNC)
diff --git a/src/test/regress/expected/window.out b/src/test/regress/expected/window.out
index de0e14a686e..891b0153004 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:  aggregate functions do not 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:  aggregate functions do not 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