diff --git a/src/backend/distributed/citus--8.4-1--8.4-2.sql b/src/backend/distributed/citus--8.4-1--8.4-2.sql
index fd95268de..e7a11b615 100644
--- a/src/backend/distributed/citus--8.4-1--8.4-2.sql
+++ b/src/backend/distributed/citus--8.4-1--8.4-2.sql
@@ -1,37 +1,37 @@
-CREATE FUNCTION stype_serialize(internal, oid, ...)serial
+CREATE FUNCTION stype_serialize(internal, oid, ...)
 RETURNS internal
 AS 'MODULE_PATHNAME'
 LANGUAGE C STRICT IMMUTABLE PARALLEL SAFE;
 
-CREATE FUNCTION stype_deserialize(internal, oid, ...)serial
+CREATE FUNCTION stype_deserialize(internal, oid, ...)
 RETURNS internal
 AS 'MODULE_PATHNAME'
 LANGUAGE C STRICT IMMUTABLE PARALLEL SAFE;
 
-CREATE FUNCTION stype_combine(internal, oid, ...)serial
+CREATE FUNCTION stype_combine(internal, oid, ...)
 RETURNS internal
 AS 'MODULE_PATHNAME'
-LANGUAGE C STRICT IMMUTABLE PARALLEL SAFE;
+LANGUAGE C PARALLEL SAFE;
 
 CREATE FUNCTION worker_partial_agg_sfunc(internal, oid, ...)
 RETURNS internal
 AS 'MODULE_PATHNAME'
-LANGUAGE C STRICT IMMUTABLE PARALLEL SAFE;
+LANGUAGE C PARALLEL SAFE;
 
 CREATE FUNCTION worker_partial_agg_ffunc(internal, oid, ...)
 RETURNS internal
 AS 'MODULE_PATHNAME'
-LANGUAGE C STRICT IMMUTABLE PARALLEL SAFE;
+LANGUAGE C PARALLEL SAFE;
 
 CREATE FUNCTION coord_combine_agg_sfunc(internal, oid, ...)
 RETURNS internal
 AS 'MODULE_PATHNAME'
-LANGUAGE C STRICT IMMUTABLE PARALLEL SAFE;
+LANGUAGE C PARALLEL SAFE;
 
 CREATE FUNCTION coord_combine_agg_ffunc(internal, oid, ...)
 RETURNS internal
 AS 'MODULE_PATHNAME'
-LANGUAGE C STRICT IMMUTABLE PARALLEL SAFE;
+LANGUAGE C PARALLEL SAFE;
 
 -- select worker_partial_agg(agg, ...)
 -- equivalent to
diff --git a/src/backend/distributed/utils/aggregate_utils.c b/src/backend/distributed/utils/aggregate_utils.c
index 7d4023105..357586102 100644
--- a/src/backend/distributed/utils/aggregate_utils.c
+++ b/src/backend/distributed/utils/aggregate_utils.c
@@ -3,6 +3,8 @@
 #include "access/htup_details.h"
 #include "catalog/pg_aggregate.h"
 #include "catalog/pg_proc.h"
+#include "catalog/pg_type.h"
+#include "utils/cache/lsyscache.h"
 #include "utils/fmgr.h"
 #include "utils/syscache.h"
 
@@ -14,35 +16,49 @@ PG_FUNCTION_INFO_V1(worker_partial_agg_ffunc);
 PG_FUNCTION_INFO_V1(coord_combine_agg_sfunc);
 PG_FUNCTION_INFO_V1(coord_combine_agg_ffunc);
 
+// TODO nodeAgg seems to decide to use serial/deserial based on stype == internal
+//      Preferably we should match that logic, instead of checking serial/deserial oids
+
 typedef struct StypeBox {
 	Datum value;
 	Oid agg;
 	bool value_null;
 } StypeBox;
 
-static Form_pg_aggregate get_aggform(Oid aggfnoid);
-static Form_pg_proc get_procform(Oid aggfnoid);
+static HeapTuple *get_aggform(Oid oid, Form_pg_aggregate *form);
+static HeapTuple *get_procform(Oid oid, Form_pg_proc *form);
+static HeapTuple *get_typeform(Oid oid, Form_pg_type *form);
 
-static Form_pg_aggregate
-get_aggform(Oid aggfnoid)
+static HeapTuple *
+get_aggform(Oid oid, Form_pg_aggregate *form)
 {
-	/* Fetch the pg_aggregate row */
-	HeapTuple tuple = SearchSysCache1(AGGFNOID, ObjectIdGetDatum(aggfnoid));
+	HeapTuple tuple = SearchSysCache1(AGGFNOID, ObjectIdGetDatum(oid));
 	if (!HeapTupleIsValid(tuple))
-		elog(ERROR, "cache lookup failed for aggregate %u",
-			 aggfnoid);
-	return (Form_pg_aggregate) GETSTRUCT(tuple);
+		elog(ERROR, "cache lookup failed for aggregate %u", oid);
+	*form = (Form_pg_aggregate) GETSTRUCT(tuple);
+	return tuple;
 }
 
-static Form_pg_proc
-get_procform(Oid fnoid)
+static HeapTuple *
+get_procform(Oid oid)
 {
-	Form_pg_proc = SearchSysCache1(PROCID, ObjectIdGetDatum(fnoid));
+	HeapTuple tuple = SearchSysCache1(PROCID, ObjectIdGetDatum(fnoid));
 	if (!HeapTupleIsValid(tuple))
-		elog(ERROR, "cache lookup failed for function %u",
-			 fnoid);
-	return (Form_pg_proc) GETSTRUCT(tuple);
+		elog(ERROR, "cache lookup failed for function %u", oid);
+	*form = (Form_pg_proc) GETSTRUCT(tuple);
+	return tuple;
 }
+
+static HeapTuple *
+get_typeform(Oid oid)
+{
+	HeapTuple tuple = SearchSysCache1(TYPEID, ObjectIdGetDatum(oid));
+	if (!HeapTupleIsValid(tuple))
+		elog(ERROR, "cache lookup failed for type %u", oid);
+	*form = (Form_pg_type) GETSTRUCT(tuple);
+	return tuple;
+}
+
 /*
  * (box) -> bytea
  * return bytes(box.agg.oid, box.agg.serial(box.value))
@@ -50,22 +66,80 @@ get_procform(Oid fnoid)
 Datum
 stypebox_serialize(PG_FUNCTION_ARGS)
 {
+	FunctionCallInfo inner_fcinfo;
+	FmgrInfo info;
 	StypeBox *box = PG_GETARG_POINTER(0);
-	Form_pg_aggregate aggform = get_aggform(box->agg);
-	// TODO return null if box null?
-	byteap *valbytes = DatumGetByteaPP(DirectFunctionCall1(aggform->serialfunc, box->value));
-	byteap *realbytes = palloc(VARSIZE(valbytes) + sizeof(Oid));
-	SET_VARSIZE(realbytes, VARSIZE(valbytes) + sizeof(Oid));
+	HeapTuple *aggtuple;
+	HeapTuple *transtypetuple;
+	Form_pg_aggregate aggform;
+	Form_pg_type transtypeform;
+	byteap *valbytes;
+	byteap *realbytes;
+	Oid serial;
+	Oid transtype;
+	Size valbyteslen_exhdr;
+	Size realbyteslen;
+	Datum result;
+
+	aggtuple = get_aggform(box->agg, &aggform);
+	serial = aggform->serialfunc;
+	transtype = aggform->aggtranstype;
+	ReleaseSysCache(aggtuple);
+
+	if (!IsValidOid(serial))
+	{
+		// TODO do we have to fallback to output/receive if not set?
+		// ie is it possible for send/recv to be unset?
+		transtypetuple = get_typeform(transtype, &transtypeform);
+		serial = transtypeform->typsend;
+		ReleaseSysCache(transtypetuple);
+	}
+
+	fmgr_info(serial, &info);
+	if (info->fn_strict && box->value_null)
+	{
+		valbytes = NULL;
+		valbyteslen_exhdr = 0;
+	}
+	else
+	{
+		InitFunctionCallInfoData(&inner_fcinfo, &info, 1, fcinfo->collation, fcinfo->context, fcinfo->resultinfo);
+		inner_fcinfo.arg[0] = box->value;
+		inner_fcinfo.argnull[0] = box->value_null;
+		result = FunctionCallInvoke(&inner_fcinfo);
+		if (inner_fcinfo.isnull)
+		{
+			valbytes = NULL;
+			valbyteslen_exhdr = 0;
+		}
+		else
+		{
+			valbytes = DatumGetByteaPP(result);
+			valbyteslen_exhdr = VARSIZE(valbytes) - VARHDRSZ;
+		}
+	}
+
+	realbyteslen = VARHDRSZ + valbyteslen_exhdr + sizeof(Oid) + sizeof(bool);
+	realbytes = palloc(realbyteslen);
+	SET_VARSIZE(realbytes, realbyteslen);
 	memcpy(VARDATA(realbytes), &box->agg, sizeof(Oid));
-	memcpy(VARDATA(realbytes) + sizeof(Oid), VARDATA(valbytes), VARSIZE(valbytes) - VARHDRSZ);
-	pfree(valbytes); // TODO I get to free this right?
+	memcpy(VARDATA(realbytes) + sizeof(Oid), &box->value_null, sizeof(bool));
+	if (valbytes != NULL)
+	{
+		memcpy(VARDATA(realbytes) + sizeof(Oid) + sizeof(bool),
+			   VARDATA(valbytes),
+			   valbyteslen_exhdr);
+		pfree(valbytes); // TODO I get to free this right?
+	}
+
 	PG_RETURN_BYTEA_P(valbytes);
 }
 
 /*
  * (bytea, internal) -> box
  * box->agg = readagg(bytea)
- * box->value = agg.deserial(readrest(bytea))
+ * box->value_null = readbool(bytea)
+ * if (!box->value_null) box->value = agg.deserial(readrest(bytea))
  * return box
  */
 Datum
@@ -73,17 +147,57 @@ stypebox_deserialize(PG_FUNCTION_ARGS)
 {
 	StypeBox *box;
 	byteap *bytes = PG_GETARG_BYTEA_PP(0);
-	byteap *inner_bytes = PG_GETARG_BYTEA_P_SLICE(0, sizeof(Oid), VARSIZE(bytes) - sizeof(Oid))
+	byteap *inner_bytes;
 	Oid agg;
+	HeapTuple *aggtuple;
+	HeapTuple *transtypetuple;
 	Form_pg_aggregate aggform;
+	Form_pg_type transtypeform;
+	Oid deserial;
+	Oid transtype;
+	Oid ioparam;
+	Oid recv;
+	StringInfoData buf;
+	bool value_null;
+
 	memcpy(&agg, VARDATA(bytes), sizeof(Oid));
-	aggform = get_aggform(agg);
-	// Can deserialize be called with NULL?
+	memcpy(&value_null, VARDATA(bytes) + sizeof(Oid), sizeof(bool));
 
 	box = palloc(sizeof(StypeBox));
 	box->agg = agg;
-	box->value = DirectFunctionCall2(aggform->deserialfunc, inner_bytes, PG_GETARG_DATUM(1));
-	box->null_value = false;
+	if (value_null)
+	{
+		box->value = (Datum) 0;
+		box->value_null = true;
+		PG_RETURN_POINTER(box);
+	}
+
+	aggtuple = get_aggform(agg, &aggform);
+	deserial = aggform->deserialfunc;
+	transtype = aggform->aggtranstype;
+	ReleaseSysCache(aggtuple);
+
+	if (aggform->deserialfunc) {
+		inner_bytes = PG_GETARG_BYTEA_P_SLICE(0, sizeof(Oid), VARSIZE(bytes) - sizeof(Oid))
+		box->value = DirectFunctionCall2(deserial, inner_bytes, PG_GETARG_DATUM(1));
+		box->null_value = false;
+	}
+	else
+	{
+		transtypetuple = get_typeform(transtype, &transtypeform);
+		ioparam = getTypeIOParam(transtypetuple);
+		recv = transtypeform->typreceive;
+		ReleaseSysCache(transtypetuple);
+
+		initStringInfo(&buf);
+		appendBinaryStringInfo(buf,
+							   VARDATA(realbytes) + sizeof(Oid) + sizeof(bool),
+							   VARSIZE(realbytes) - VARHDRSZ - sizeof(Oid) - sizeof(bool));
+
+		box->value = OidReceiveFunctionCall(recv, &buf, ioparam, -1);
+		box->value_null = value_null;
+	}
+
 	PG_RETURN_POINTER(box);
 }
 
@@ -98,9 +212,10 @@ stypebox_combine(PG_FUNCTION_ARGS)
 	StypeBox *box1 = NULL;
 	StypeBox *box2 = NULL;
 	FunctionCallInfo inner_fcinfo;
+	FmgrInfo info;
 	Oid aggOid;
+	HeapTuple *aggtuple;
 	Form_pg_aggregate aggform;
-	Form_pg_proc combineform;
 
 	if (!PG_ISARGNULL(0))
 	{
@@ -123,13 +238,14 @@ stypebox_combine(PG_FUNCTION_ARGS)
 		box1->agg = box2->agg;
 	}
 
-	aggform = get_aggform(box->agg);
-	combineform = get_procform(aggform->combinefn);
-
-	// TODO respect strictness
+	aggtuple = get_aggform(box1->agg, &aggform);
 	Assert(IsValidOid(aggform->combineefn));
+	combine = aggform->combinefn;
+	ReleaseSysCache(aggtuple);
 
-	if (combineform->proisstrict)
+	fmgr_info(combine, &info);
+
+	if (info.fn_strict)
 	{
 		if (box1->value_null)
 		{
@@ -145,14 +261,15 @@ stypebox_combine(PG_FUNCTION_ARGS)
 		}
 	}
 
-	InitFunctionCallInfoData(&inner_fcinfo, &info, fcinfo->nargs - 1, fcinfo->collation, fcinfo->context, fcinfo->resultinfo);
+	InitFunctionCallInfoData(&inner_fcinfo, &info, 2, fcinfo->collation, fcinfo->context, fcinfo->resultinfo);
 	inner_fcinfo.arg[0] = box1->value;
 	inner_fcinfo.argnull[0] = box1->value_null;
 	inner_fcinfo.arg[1] = box2->value;
 	inner_fcinfo.argnull[1] = box2->value_null;
 	// TODO Deal with memory management juggling (see executor/nodeAgg)
-	box1->value = FunctionCallInvoke(inner_fcinfo);
+	box1->value = FunctionCallInvoke(&inner_fcinfo);
 	box1->value_null = inner_fcinfo.isnull;
+
 	PG_RETURN_POINTER(box1);
 }
 
@@ -174,19 +291,33 @@ worker_partial_agg_sfunc(PG_FUNCTION_ARGS)
 		box->agg = PG_GETARG_OID(1);
 		box->value = (Datum) 0;
 		box->value_null = true;
-	} else {
+	}
+	else
+	{
 		box = PG_GETARG_POINTER(0);
 		Assert(box->agg == PG_GETARG_OID(1));
 	}
 	fmgr_info(box->agg, &info);
 	InitFunctionCallInfoData(&inner_fcinfo, &info, fcinfo->nargs - 1, fcinfo->collation, fcinfo->context, fcinfo->resultinfo);
-	// TODO if strict, deal with it
+	if (info.flinfo->fn_strict) {
+		if (box->value_null)
+		{
+			PG_RETURN_NULL();
+		}
+		for (i = 2; i<PG_NARGS(); i++)
+		{
+			if (PG_ARGISNULL(i))
+			{
+				PG_RETURN_NULL();
+			}
+		}
+	}
 	// Deal with memory management juggling (see executor/nodeAgg)
 	inner_fcinfo.arg[0] = box->value;
 	inner_fcinfo.argnull[0] = box->value_null;
 	memcpy(&inner_fcinfo.arg[1], &fcinfo.arg[2], sizeof(Datum) * (inner_fcinfo.nargs - 1));
 	memcpy(&inner_fcinfo.argnull[1], &fcinfo.argnull[2], sizeof(bool) * (inner_fcinfo.nargs - 1));
-	box->value = FunctionCallInvoke(inner_fcinfo);
+	box->value = FunctionCallInvoke(&inner_fcinfo);
 	box->value_null = inner_fcinfo.isnull;
 	PG_RETURN_POINTER(box);
 }
@@ -198,48 +329,201 @@ worker_partial_agg_sfunc(PG_FUNCTION_ARGS)
 Datum
 worker_partial_agg_ffunc(PG_FUNCTION_ARGS)
 {
+	FunctionCallInfo inner_fcinfo;
+	FmgrInfo info;
 	StypeBox *box = PG_GETARG_POINTER(0);
-	Form_pg_aggregate aggform = get_aggform(box->agg);
-	PG_RETURN_DATUM(DirectFunctionCall1(aggform->serialfunc, box->value));
+	HeapTuple *aggtuple;
+	Form_pg_aggregate aggform;
+	Oid serial;
+	Datum result;
+
+	aggtuple = get_aggform(box->agg);
+	serial = aggform->serialfunc;
+	ReleaseSysCache(aggtuple);
+
+	if (IsValidOid(serial))
+	{
+		fmgr_info(serial, &info);
+		if (info->fn_strict && box->value_null)
+		{
+			PG_RETURN_NULL();
+		}
+		InitFunctionCallInfoData(&inner_fcinfo, &info, 1, fcinfo->collation, fcinfo->context, fcinfo->resultinfo);
+		inner_fcinfo.arg[0] = box->value;
+		inner_fcinfo.argnull[0] = box->value_null;
+		result = FunctionCallInvoke(&inner_fcinfo);
+		if (inner_fcinfo.isnull)
+		{
+			PG_RETURN_NULL();
+		}
+		PG_RETURN_DATUM(result);
+	}
+	else
+	{
+		if (box->value_null)
+		{
+			PG_RETURN_NULL();
+		}
+		PG_RETURN_DATUM(box->value);
+	}
 }
 
 /*
- * (box, agg, valbytes) -> box
+ * (box, agg, valbytes|value) -> box
  * box->agg = agg
- * box->value = agg.sfunc(box->value, agg.deserialize(valbytes))
+ * if agg.deserialize: box->value = agg.combine(box->value, agg.deserialize(valbytes))
+ * else: box->value = agg.combine(box->value, value)
  * return box
  */
 Datum
 coord_combine_agg_sfunc(PG_FUNCTION_ARGS)
 {
-	// TODO
+	FunctionCallInfo inner_fcinfo;
+	FmgrInfo info;
+	HeapTuple *aggtuple;
+	HeapTuple *transtypetuple;
+	Form_pg_aggregate aggform;
+	Form_pg_type transtypeform;
+	Oid combine;
+	Oid deserial;
+	Datum value;
+	bool value_null;
+
+	if (PG_ARGISNULL(0)) {
+		box = palloc(sizeof(StypeBox));
+		box->agg = PG_GETARG_OID(1);
+		box->value = (Datum) 0;
+		box->value_null = true;
+	}
+	else
+	{
+		box = PG_GETARG_POINTER(0);
+		Assert(box->agg == PG_GETARG_OID(1));
+	}
+
+	aggtuple = get_aggform(box->agg, &aggform);
+	deserial = aggform->deserialfunc;
+	combine = aggform->combinefn;
+	ReleaseSysCache(aggtuple);
+
+	value_null = PG_ISARGNULL(2);
+	if (IsOidValid(deserial))
+	{
+		fmgr_info(deserial, &info);
+		if (!value_null || !info->fn_strict)
+		{
+			InitFunctionCallInfoData(&inner_fcinfo, &info, 2, fcinfo->collation, fcinfo->context, fcinfo->resultinfo);
+			inner_fcinfo.arg[0] = value_null ? 0 (Datum) : PG_GETARG_BYTEA_PP(2);
+			inner_fcinfo.arg[1] = 0 (Datum);
+			inner_fcinfo.argnull[0] = value_null;
+			inner_fcinfo.argnull[1] = true;
+			value = FunctionCallInvoke(&inner_fcinfo);
+			value_null = inner_fcinfo.isnull;
+		}
+		else
+		{
+			value = (Datum) 0;
+		}
+	}
+	else
+	{
+		value = value_null ? (Datum) 0 : PG_GETARG(2);
+	}
+
+	fmgr_info(combine, &info);
+
+	if (info.fn_strict) {
+		if (box->value_null)
+		{
+			if (value_null)
+			{
+				PG_RETURN_NULL();
+			}
+			box->value = value;
+			box->value_null = false;
+			PG_RETURN_POINTER(box);
+		}
+		if (value_null)
+		{
+			PG_RETURN_POINTER(box);
+		}
+	}
+
+	InitFunctionCallInfoData(&innerfcinfo, &info, 2, fcinfo->collation, fcinfo->context, fcinfo->resultinfo);
+	inner_fcinfo.arg[0] = box->value;
+	inner_fcinfo.argnull[0] = box->value_null;
+	inner_fcinfo.arg[1] = value;
+	inner_fcinfo.argnull[1] = value_null;
+	box->value = DirectFunctionCall2(combine, box->value, value);
+	box->value = FunctionCallInvoke(&inner_fcinfo);
+	box->value_null = inner_fcinfo.isnull;
+
+	PG_RETURN_POINTER(box);
 }
 
 /*
- * box -> fval
+ * (box, ...) -> fval
  * return box.agg.ffunc(box.value)
  */
 Datum
 coord_combine_agg_ffunc(PG_FUNCTION_ARGS)
 {
-	StypeBox = PG_GETARG_POINTER(0);
+	Datum ret;
+	StypeBox *box = PG_GETARG_POINTER(0);
 	FunctionCallInfo inner_fcinfo;
 	FmgrInfo info;
-	Form_pg_aggregate aggform = get_aggform(box->agg);
+	int inner_nargs;
+	HeapTuple *aggtuple;
+	HeapTuple *ffunctuple;
+	Form_pg_aggregate aggform;
 	Form_pg_proc ffuncform;
+	Oid ffunc;
+	bool fextra;
+	bool final_strict;
+	int i;
 
-	if (!IsValidOid(aggform->aggfinalfn))
+	aggtuple = get_aggform(box->agg, &aggform);
+	ffunc = aggform->aggfinalfn;
+	fextra = aggform->aggfinalextra;
+	ReleaseSysCache(aggtuple);
+
+	if (!IsValidOid(ffunc))
 	{
-		if (box->value_null) {
-			return NULL;
+		if (box->value_null)
+		{
+			PG_RETURN_NULL();
 		}
 		PG_RETURN_DATUM(box->value);
 	}
 
-	ffuncform = get_aggform(aggform->aggfinalfn);
-	// TODO FINALFUNC EXTRA & stuff
-	fmgr_info(aggform->aggfinalfn, &info);
-	InitFunctionCallInfoData(&inner_fcinfo, &info, fcinfo->nargs - 1, fcinfo->collation, fcinfo->context, fcinfo->resultinfo);
+	ffunctuple = get_procform(ffunc, &ffuncform);
+	final_strict = ffuncform->proisstrict;
+	ReleaseSysCache(ffunctuple);
 
+	if (final_strict && box->value_null)
+	{
+		PG_RETURN_NULL();
+	}
+
+	fmgr_info(ffunc, &info);
+	if (fextra)
+	{
+		inner_nargs = fcinfo->nargs;
+	}
+	else
+	{
+		inner_nargs = 1;
+	}
+	fmgr_info(ffunc, &info);
+	InitFunctionCallInfoData(&inner_fcinfo, &info, inner_nargs, fcinfo->collation, fcinfo->context, fcinfo->resultinfo);
+	inner_fcinfo.arg[0] = box->value;
+	inner_fcinfo.argnull[0] = box->value_null;
+	for (i = 1; i<inner_nargs; i++)
+	{
+		inner_fcinfo.argnull[i] = true;
+	}
+	ret = FunctionCallInvoke(&inner_fcinfo);
+	fcinfo.isnull = inner_fcinfo.isnull;
+	return ret;
 }