diff --git a/src/backend/parser/parse_agg.c b/src/backend/parser/parse_agg.c
index 81e1d70ffc1..5e942075444 100644
--- a/src/backend/parser/parse_agg.c
+++ b/src/backend/parser/parse_agg.c
@@ -1110,7 +1110,8 @@ transformWindowFuncCall(ParseState *pstate, WindowFunc *wfunc,
 				equal(refwin->orderClause, windef->orderClause) &&
 				refwin->frameOptions == windef->frameOptions &&
 				equal(refwin->startOffset, windef->startOffset) &&
-				equal(refwin->endOffset, windef->endOffset))
+				equal(refwin->endOffset, windef->endOffset) &&
+				equal(refwin->rpCommonSyntax, windef->rpCommonSyntax))
 			{
 				/* found a duplicate window specification */
 				wfunc->winref = winref;