diff --git a/src/backend/executor/nodeAgg.c b/src/backend/executor/nodeAgg.c
index d26ce0847a0b6ef401c6cb85fbe8b2d522f3c7fe..da6ef1a94c419704fe7ef07963d0fd70eebd821a 100644
--- a/src/backend/executor/nodeAgg.c
+++ b/src/backend/executor/nodeAgg.c
@@ -1246,6 +1246,17 @@ advance_combine_function(AggState *aggstate,
 			pergroupstate->noTransValue = false;
 			return;
 		}
+
+		if (pergroupstate->transValueIsNull)
+		{
+			/*
+			 * Don't call a strict function with NULL inputs.  Note it is
+			 * possible to get here despite the above tests, if the combinefn
+			 * is strict *and* returned a NULL on a prior cycle. If that
+			 * happens we will propagate the NULL all the way to the end.
+			 */
+			return;
+		}
 	}
 
 	/* We run the combine functions in per-input-tuple memory context */
diff --git a/src/test/regress/expected/aggregates.out b/src/test/regress/expected/aggregates.out
index 3408cf3333e2e6f4e003673c195ce002412a13e4..f8c42f911b5d8b2a4fd3c140011fd7f14c727aad 100644
--- a/src/test/regress/expected/aggregates.out
+++ b/src/test/regress/expected/aggregates.out
@@ -1993,3 +1993,74 @@ NOTICE:  sum_transfn called with 4
 (1 row)
 
 rollback;
+-- test that the aggregate transition logic correctly handles
+-- transition / combine functions returning NULL
+-- First test the case of a normal transition function returning NULL
+BEGIN;
+CREATE FUNCTION balkifnull(int8, int4)
+RETURNS int8
+STRICT
+LANGUAGE plpgsql AS $$
+BEGIN
+    IF $1 IS NULL THEN
+       RAISE 'erroneously called with NULL argument';
+    END IF;
+    RETURN NULL;
+END$$;
+CREATE AGGREGATE balk(
+    BASETYPE = int4,
+    SFUNC = balkifnull(int8, int4),
+    STYPE = int8,
+    "PARALLEL" = SAFE,
+    INITCOND = '0');
+SELECT balk(1) FROM tenk1;
+ balk 
+------
+     
+(1 row)
+
+ROLLBACK;
+-- Secondly test the case of a parallel aggregate combiner function
+-- returning NULL. For that use normal transition function, but a
+-- combiner function returning NULL.
+BEGIN ISOLATION LEVEL REPEATABLE READ;
+CREATE FUNCTION balkifnull(int8, int8)
+RETURNS int8
+PARALLEL SAFE
+STRICT
+LANGUAGE plpgsql AS $$
+BEGIN
+    IF $1 IS NULL THEN
+       RAISE 'erroneously called with NULL argument';
+    END IF;
+    RETURN NULL;
+END$$;
+CREATE AGGREGATE balk(
+    BASETYPE = int4,
+    SFUNC = int4_sum(int8, int4),
+    STYPE = int8,
+    COMBINEFUNC = balkifnull(int8, int8),
+    "PARALLEL" = SAFE,
+    INITCOND = '0'
+);
+-- force use of parallelism
+ALTER TABLE tenk1 set (parallel_workers = 4);
+SET LOCAL parallel_setup_cost=0;
+SET LOCAL max_parallel_workers_per_gather=4;
+EXPLAIN (COSTS OFF) SELECT balk(1) FROM tenk1;
+                                   QUERY PLAN                                   
+--------------------------------------------------------------------------------
+ Finalize Aggregate
+   ->  Gather
+         Workers Planned: 4
+         ->  Partial Aggregate
+               ->  Parallel Index Only Scan using tenk1_thous_tenthous on tenk1
+(5 rows)
+
+SELECT balk(1) FROM tenk1;
+ balk 
+------
+     
+(1 row)
+
+ROLLBACK;
diff --git a/src/test/regress/sql/aggregates.sql b/src/test/regress/sql/aggregates.sql
index 55c8528fd57575a3a8f3c098df282ba2977fb245..1bfc5e649c30bfa17b756a907b6fde58d89641e4 100644
--- a/src/test/regress/sql/aggregates.sql
+++ b/src/test/regress/sql/aggregates.sql
@@ -843,3 +843,66 @@ create aggregate my_half_sum(int4)
 select my_sum(one),my_half_sum(one) from (values(1),(2),(3),(4)) t(one);
 
 rollback;
+
+
+-- test that the aggregate transition logic correctly handles
+-- transition / combine functions returning NULL
+
+-- First test the case of a normal transition function returning NULL
+BEGIN;
+CREATE FUNCTION balkifnull(int8, int4)
+RETURNS int8
+STRICT
+LANGUAGE plpgsql AS $$
+BEGIN
+    IF $1 IS NULL THEN
+       RAISE 'erroneously called with NULL argument';
+    END IF;
+    RETURN NULL;
+END$$;
+
+CREATE AGGREGATE balk(
+    BASETYPE = int4,
+    SFUNC = balkifnull(int8, int4),
+    STYPE = int8,
+    "PARALLEL" = SAFE,
+    INITCOND = '0');
+
+SELECT balk(1) FROM tenk1;
+
+ROLLBACK;
+
+-- Secondly test the case of a parallel aggregate combiner function
+-- returning NULL. For that use normal transition function, but a
+-- combiner function returning NULL.
+BEGIN ISOLATION LEVEL REPEATABLE READ;
+CREATE FUNCTION balkifnull(int8, int8)
+RETURNS int8
+PARALLEL SAFE
+STRICT
+LANGUAGE plpgsql AS $$
+BEGIN
+    IF $1 IS NULL THEN
+       RAISE 'erroneously called with NULL argument';
+    END IF;
+    RETURN NULL;
+END$$;
+
+CREATE AGGREGATE balk(
+    BASETYPE = int4,
+    SFUNC = int4_sum(int8, int4),
+    STYPE = int8,
+    COMBINEFUNC = balkifnull(int8, int8),
+    "PARALLEL" = SAFE,
+    INITCOND = '0'
+);
+
+-- force use of parallelism
+ALTER TABLE tenk1 set (parallel_workers = 4);
+SET LOCAL parallel_setup_cost=0;
+SET LOCAL max_parallel_workers_per_gather=4;
+
+EXPLAIN (COSTS OFF) SELECT balk(1) FROM tenk1;
+SELECT balk(1) FROM tenk1;
+
+ROLLBACK;