diff --git a/src/backend/executor/nodeWindowAgg.c b/src/backend/executor/nodeWindowAgg.c
index 371548ceb3..96c8527eb3 100644
--- a/src/backend/executor/nodeWindowAgg.c
+++ b/src/backend/executor/nodeWindowAgg.c
@@ -2218,7 +2218,7 @@ initialize_peragg(WindowAggState *winstate, WindowFunc *wfunc,
 								 numArguments,
 								 0,		/* no ordered-set window functions yet */
 								 false, /* no variadic window functions yet */
-								 wfunc->wintype,
+								 aggtranstype,
 								 wfunc->inputcollid,
 								 transfn_oid,
 								 invtransfn_oid,
diff --git a/src/test/regress/expected/polymorphism.out b/src/test/regress/expected/polymorphism.out
index ddf45cf597..68b88d33a1 100644
--- a/src/test/regress/expected/polymorphism.out
+++ b/src/test/regress/expected/polymorphism.out
@@ -635,6 +635,61 @@ create aggregate build_group(int8, integer) (
   SFUNC = add_group,
   STYPE = int8[]
 );
+-- check proper resolution of data types for polymorphic transfn/finalfn
+create function first_el(anyarray) returns anyelement as
+'select $1[1]' language sql strict immutable;
+create aggregate first_el_agg_f8(float8) (
+  SFUNC = array_append,
+  STYPE = float8[],
+  FINALFUNC = first_el
+);
+create aggregate first_el_agg_any(anyelement) (
+  SFUNC = array_append,
+  STYPE = anyarray,
+  FINALFUNC = first_el
+);
+select first_el_agg_f8(x::float8) from generate_series(1,10) x;
+ first_el_agg_f8 
+-----------------
+               1
+(1 row)
+
+select first_el_agg_any(x) from generate_series(1,10) x;
+ first_el_agg_any 
+------------------
+                1
+(1 row)
+
+select first_el_agg_f8(x::float8) over(order by x) from generate_series(1,10) x;
+ first_el_agg_f8 
+-----------------
+               1
+               1
+               1
+               1
+               1
+               1
+               1
+               1
+               1
+               1
+(10 rows)
+
+select first_el_agg_any(x) over(order by x) from generate_series(1,10) x;
+ first_el_agg_any 
+------------------
+                1
+                1
+                1
+                1
+                1
+                1
+                1
+                1
+                1
+                1
+(10 rows)
+
 -- check that we can apply functions taking ANYARRAY to pg_stats
 select distinct array_ndims(histogram_bounds) from pg_stats
 where histogram_bounds is not null;
diff --git a/src/test/regress/sql/polymorphism.sql b/src/test/regress/sql/polymorphism.sql
index 72f6cb5e7c..45ae7a23aa 100644
--- a/src/test/regress/sql/polymorphism.sql
+++ b/src/test/regress/sql/polymorphism.sql
@@ -443,6 +443,28 @@ create aggregate build_group(int8, integer) (
   STYPE = int8[]
 );
 
+-- check proper resolution of data types for polymorphic transfn/finalfn
+
+create function first_el(anyarray) returns anyelement as
+'select $1[1]' language sql strict immutable;
+
+create aggregate first_el_agg_f8(float8) (
+  SFUNC = array_append,
+  STYPE = float8[],
+  FINALFUNC = first_el
+);
+
+create aggregate first_el_agg_any(anyelement) (
+  SFUNC = array_append,
+  STYPE = anyarray,
+  FINALFUNC = first_el
+);
+
+select first_el_agg_f8(x::float8) from generate_series(1,10) x;
+select first_el_agg_any(x) from generate_series(1,10) x;
+select first_el_agg_f8(x::float8) over(order by x) from generate_series(1,10) x;
+select first_el_agg_any(x) over(order by x) from generate_series(1,10) x;
+
 -- check that we can apply functions taking ANYARRAY to pg_stats
 select distinct array_ndims(histogram_bounds) from pg_stats
 where histogram_bounds is not null;