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 9449077cf..fd95268de 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
@@ -40,7 +40,6 @@ CREATE AGGREGATE worker_partial_agg(oid, ...) (
 	STYPE = internal,
 	SFUNC = worker_partial_agg_sfunc,
 	FINALFUNC = worker_partial_agg_ffunc,
-	FINALFUNC_EXTRA,
 	COMBINEFUNC = stypebox_combine,
 	SERIALFUNC = stypebox_serialize,
 	DESERIALFUNC = stypebox_deserialize,
diff --git a/src/backend/distributed/utils/aggregate_utils.c b/src/backend/distributed/utils/aggregate_utils.c
index 54efdce30..7d4023105 100644
--- a/src/backend/distributed/utils/aggregate_utils.c
+++ b/src/backend/distributed/utils/aggregate_utils.c
@@ -1,6 +1,10 @@
 #include "postgres.h"
 
+#include "access/htup_details.h"
+#include "catalog/pg_aggregate.h"
+#include "catalog/pg_proc.h"
 #include "utils/fmgr.h"
+#include "utils/syscache.h"
 
 PG_FUNCTION_INFO_V1(stypebox_serialize);
 PG_FUNCTION_INFO_V1(stypebox_deserialize);
@@ -12,17 +16,50 @@ PG_FUNCTION_INFO_V1(coord_combine_agg_ffunc);
 
 typedef struct StypeBox {
 	Datum value;
-	bool value_null;
 	Oid agg;
+	bool value_null;
 } StypeBox;
 
+static Form_pg_aggregate get_aggform(Oid aggfnoid);
+static Form_pg_proc get_procform(Oid aggfnoid);
+
+static Form_pg_aggregate
+get_aggform(Oid aggfnoid)
+{
+	/* Fetch the pg_aggregate row */
+	HeapTuple tuple = SearchSysCache1(AGGFNOID, ObjectIdGetDatum(aggfnoid));
+	if (!HeapTupleIsValid(tuple))
+		elog(ERROR, "cache lookup failed for aggregate %u",
+			 aggfnoid);
+	return (Form_pg_aggregate) GETSTRUCT(tuple);
+}
+
+static Form_pg_proc
+get_procform(Oid fnoid)
+{
+	Form_pg_proc = SearchSysCache1(PROCID, ObjectIdGetDatum(fnoid));
+	if (!HeapTupleIsValid(tuple))
+		elog(ERROR, "cache lookup failed for function %u",
+			 fnoid);
+	return (Form_pg_proc) GETSTRUCT(tuple);
+}
 /*
  * (box) -> bytea
- * return bytes(box.agg.name, box.agg.serial(box.value))
+ * return bytes(box.agg.oid, box.agg.serial(box.value))
  */
 Datum
 stypebox_serialize(PG_FUNCTION_ARGS)
 {
+	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));
+	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?
+	PG_RETURN_BYTEA_P(valbytes);
 }
 
 /*
@@ -34,6 +71,20 @@ stypebox_serialize(PG_FUNCTION_ARGS)
 Datum
 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))
+	Oid agg;
+	Form_pg_aggregate aggform;
+	memcpy(&agg, VARDATA(bytes), sizeof(Oid));
+	aggform = get_aggform(agg);
+	// Can deserialize be called with NULL?
+
+	box = palloc(sizeof(StypeBox));
+	box->agg = agg;
+	box->value = DirectFunctionCall2(aggform->deserialfunc, inner_bytes, PG_GETARG_DATUM(1));
+	box->null_value = false;
+	PG_RETURN_POINTER(box);
 }
 
 /*
@@ -46,7 +97,11 @@ stypebox_combine(PG_FUNCTION_ARGS)
 {
 	StypeBox *box1 = NULL;
 	StypeBox *box2 = NULL;
+	FunctionCallInfo inner_fcinfo;
 	Oid aggOid;
+	Form_pg_aggregate aggform;
+	Form_pg_proc combineform;
+
 	if (!PG_ISARGNULL(0))
 	{
 		box1 = PG_GETARG_POINTER(0);
@@ -55,6 +110,7 @@ stypebox_combine(PG_FUNCTION_ARGS)
 	{
 		box2 = PG_GETARG_POINTER(1);
 	}
+
 	if (box1 == NULL)
 	{
 		if (box2 == NULL)
@@ -66,8 +122,37 @@ stypebox_combine(PG_FUNCTION_ARGS)
 		box1->value_null = true;
 		box1->agg = box2->agg;
 	}
-	// TODO
-	// box1.agg = box1.agg.combine(box1.value, box2.value)
+
+	aggform = get_aggform(box->agg);
+	combineform = get_procform(aggform->combinefn);
+
+	// TODO respect strictness
+	Assert(IsValidOid(aggform->combineefn));
+
+	if (combineform->proisstrict)
+	{
+		if (box1->value_null)
+		{
+			if (box2->value_null)
+			{
+				PG_RETURN_NULL();
+			}
+			PG_RETURN_DATUM(box2->value);
+		}
+		if (box2->value_null)
+		{
+			PG_RETURN_DATUM(box1->value);
+		}
+	}
+
+	InitFunctionCallInfoData(&inner_fcinfo, &info, fcinfo->nargs - 1, 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_null = inner_fcinfo.isnull;
 	PG_RETURN_POINTER(box1);
 }
 
@@ -81,6 +166,8 @@ Datum
 worker_partial_agg_sfunc(PG_FUNCTION_ARGS)
 {
 	StypeBox *box;
+	FunctionCallInfo inner_fcinfo;
+	FmgrInfo info;
 	int i;
 	if (PG_ARGISNULL(0)) {
 		box = palloc(sizeof(StypeBox));
@@ -91,9 +178,7 @@ worker_partial_agg_sfunc(PG_FUNCTION_ARGS)
 		box = PG_GETARG_POINTER(0);
 		Assert(box->agg == PG_GETARG_OID(1));
 	}
-	FmgrInfo info;
 	fmgr_info(box->agg, &info);
-	FunctionCallInfo inner_fcinfo;
 	InitFunctionCallInfoData(&inner_fcinfo, &info, fcinfo->nargs - 1, fcinfo->collation, fcinfo->context, fcinfo->resultinfo);
 	// TODO if strict, deal with it
 	// Deal with memory management juggling (see executor/nodeAgg)
@@ -113,12 +198,48 @@ worker_partial_agg_sfunc(PG_FUNCTION_ARGS)
 Datum
 worker_partial_agg_ffunc(PG_FUNCTION_ARGS)
 {
+	StypeBox *box = PG_GETARG_POINTER(0);
+	Form_pg_aggregate aggform = get_aggform(box->agg);
+	PG_RETURN_DATUM(DirectFunctionCall1(aggform->serialfunc, box->value));
 }
 
 /*
  * (box, agg, valbytes) -> box
+ * box->agg = agg
+ * box->value = agg.sfunc(box->value, agg.deserialize(valbytes))
+ * return box
  */
 Datum
 coord_combine_agg_sfunc(PG_FUNCTION_ARGS)
 {
+	// TODO
 }
+
+/*
+ * box -> fval
+ * return box.agg.ffunc(box.value)
+ */
+Datum
+coord_combine_agg_ffunc(PG_FUNCTION_ARGS)
+{
+	StypeBox = PG_GETARG_POINTER(0);
+	FunctionCallInfo inner_fcinfo;
+	FmgrInfo info;
+	Form_pg_aggregate aggform = get_aggform(box->agg);
+	Form_pg_proc ffuncform;
+
+	if (!IsValidOid(aggform->aggfinalfn))
+	{
+		if (box->value_null) {
+			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);
+
+}
+