diff --git a/src/backend/executor/nodeAgg.c b/src/backend/executor/nodeAgg.c
index af93b4db6c0..70fb457f930 100644
--- a/src/backend/executor/nodeAgg.c
+++ b/src/backend/executor/nodeAgg.c
@@ -2907,12 +2907,6 @@ build_pertrans_for_aggref(AggStatePerTrans pertrans,
 
 	pertrans->aggtranstype = aggtranstype;
 
-	/* Detect how many arguments to pass to the transfn */
-	if (AGGKIND_IS_ORDERED_SET(aggref->aggkind))
-		pertrans->numTransInputs = numInputs;
-	else
-		pertrans->numTransInputs = numArguments;
-
 	/*
 	 * When combining states, we have no use at all for the aggregate
 	 * function's transfn. Instead we use the combinefn.  In this case, the
@@ -2922,6 +2916,17 @@ build_pertrans_for_aggref(AggStatePerTrans pertrans,
 	if (DO_AGGSPLIT_COMBINE(aggstate->aggsplit))
 	{
 		Expr	   *combinefnexpr;
+		size_t		numTransArgs;
+
+		/*
+		 * When combining there's only one input, the to-be-combined added
+		 * transition value from below (this node's transition value is
+		 * counted separately).
+		 */
+		pertrans->numTransInputs = 1;
+
+		/* account for the current transition state */
+		numTransArgs = pertrans->numTransInputs + 1;
 
 		build_aggregate_combinefn_expr(aggtranstype,
 									   aggref->inputcollid,
@@ -2932,7 +2937,7 @@ build_pertrans_for_aggref(AggStatePerTrans pertrans,
 
 		InitFunctionCallInfoData(pertrans->transfn_fcinfo,
 								 &pertrans->transfn,
-								 2,
+								 numTransArgs,
 								 pertrans->aggCollation,
 								 (void *) aggstate, NULL);
 
@@ -2950,6 +2955,16 @@ build_pertrans_for_aggref(AggStatePerTrans pertrans,
 	else
 	{
 		Expr	   *transfnexpr;
+		size_t		numTransArgs;
+
+		/* Detect how many arguments to pass to the transfn */
+		if (AGGKIND_IS_ORDERED_SET(aggref->aggkind))
+			pertrans->numTransInputs = numInputs;
+		else
+			pertrans->numTransInputs = numArguments;
+
+		/* account for the current transition state */
+		numTransArgs = pertrans->numTransInputs + 1;
 
 		/*
 		 * Set up infrastructure for calling the transfn.  Note that invtrans
@@ -2970,7 +2985,7 @@ build_pertrans_for_aggref(AggStatePerTrans pertrans,
 
 		InitFunctionCallInfoData(pertrans->transfn_fcinfo,
 								 &pertrans->transfn,
-								 pertrans->numTransInputs + 1,
+								 numTransArgs,
 								 pertrans->aggCollation,
 								 (void *) aggstate, NULL);
 
diff --git a/src/test/regress/expected/aggregates.out b/src/test/regress/expected/aggregates.out
index deed5bef469..637aee14fca 100644
--- a/src/test/regress/expected/aggregates.out
+++ b/src/test/regress/expected/aggregates.out
@@ -2074,21 +2074,26 @@ SET max_parallel_workers_per_gather = 4;
 SET enable_indexonlyscan = off;
 -- variance(int4) covers numeric_poly_combine
 -- sum(int8) covers int8_avg_combine
-EXPLAIN (COSTS OFF)
-  SELECT variance(unique1::int4), sum(unique1::int8) FROM tenk1;
-                  QUERY PLAN                  
-----------------------------------------------
+-- regr_count(float8, float8) covers int8inc_float8_float8 and aggregates with > 1 arg
+EXPLAIN (COSTS OFF, VERBOSE)
+  SELECT variance(unique1::int4), sum(unique1::int8), regr_count(unique1::float8, unique1::float8) FROM tenk1;
+                                                                            QUERY PLAN                                                                             
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------
  Finalize Aggregate
+   Output: variance(unique1), sum((unique1)::bigint), regr_count((unique1)::double precision, (unique1)::double precision)
    ->  Gather
+         Output: (PARTIAL variance(unique1)), (PARTIAL sum((unique1)::bigint)), (PARTIAL regr_count((unique1)::double precision, (unique1)::double precision))
          Workers Planned: 4
          ->  Partial Aggregate
-               ->  Parallel Seq Scan on tenk1
-(5 rows)
+               Output: PARTIAL variance(unique1), PARTIAL sum((unique1)::bigint), PARTIAL regr_count((unique1)::double precision, (unique1)::double precision)
+               ->  Parallel Seq Scan on public.tenk1
+                     Output: unique1, unique2, two, four, ten, twenty, hundred, thousand, twothousand, fivethous, tenthous, odd, even, stringu1, stringu2, string4
+(9 rows)
 
-SELECT variance(unique1::int4), sum(unique1::int8) FROM tenk1;
-       variance       |   sum    
-----------------------+----------
- 8334166.666666666667 | 49995000
+SELECT variance(unique1::int4), sum(unique1::int8), regr_count(unique1::float8, unique1::float8) FROM tenk1;
+       variance       |   sum    | regr_count 
+----------------------+----------+------------
+ 8334166.666666666667 | 49995000 |      10000
 (1 row)
 
 ROLLBACK;
diff --git a/src/test/regress/sql/aggregates.sql b/src/test/regress/sql/aggregates.sql
index a03f897bcc2..f22dd776f41 100644
--- a/src/test/regress/sql/aggregates.sql
+++ b/src/test/regress/sql/aggregates.sql
@@ -919,10 +919,11 @@ SET enable_indexonlyscan = off;
 
 -- variance(int4) covers numeric_poly_combine
 -- sum(int8) covers int8_avg_combine
-EXPLAIN (COSTS OFF)
-  SELECT variance(unique1::int4), sum(unique1::int8) FROM tenk1;
+-- regr_count(float8, float8) covers int8inc_float8_float8 and aggregates with > 1 arg
+EXPLAIN (COSTS OFF, VERBOSE)
+  SELECT variance(unique1::int4), sum(unique1::int8), regr_count(unique1::float8, unique1::float8) FROM tenk1;
 
-SELECT variance(unique1::int4), sum(unique1::int8) FROM tenk1;
+SELECT variance(unique1::int4), sum(unique1::int8), regr_count(unique1::float8, unique1::float8) FROM tenk1;
 
 ROLLBACK;