diff --git a/.unreleased/bugfix_5990 b/.unreleased/bugfix_5990
new file mode 100644
index 00000000000..39513242393
--- /dev/null
+++ b/.unreleased/bugfix_5990
@@ -0,0 +1 @@
+Fixes: #5990 Place data in first/last function in correct mctx 
diff --git a/src/agg_bookend.c b/src/agg_bookend.c
index ae163c646f5..90cd4e556aa 100644
--- a/src/agg_bookend.c
+++ b/src/agg_bookend.c
@@ -137,18 +137,17 @@ polydatum_deserialize_type(StringInfo buf)
  *
  */
 static PolyDatum *
-polydatum_deserialize(PolyDatum *result, StringInfo buf, PolyDatumIOState *state,
-					  FunctionCallInfo fcinfo)
+polydatum_deserialize(MemoryContext mem_ctx, PolyDatum *result, StringInfo buf,
+					  PolyDatumIOState *state, FunctionCallInfo fcinfo)
 {
 	int itemlen;
 	StringInfoData item_buf;
 	StringInfo bufptr;
 	char csave;
 
-	if (result == NULL)
-	{
-		result = palloc(sizeof(PolyDatum));
-	}
+	Assert(result != NULL);
+
+	MemoryContext old_context = MemoryContextSwitchTo(mem_ctx);
 
 	result->type_oid = polydatum_deserialize_type(buf);
 
@@ -212,6 +211,9 @@ polydatum_deserialize(PolyDatum *result, StringInfo buf, PolyDatumIOState *state
 
 		buf->data[buf->cursor] = csave;
 	}
+
+	MemoryContextSwitchTo(old_context);
+
 	return result;
 }
 
@@ -511,12 +513,13 @@ ts_bookend_serializefunc(PG_FUNCTION_ARGS)
 Datum
 ts_bookend_deserializefunc(PG_FUNCTION_ARGS)
 {
+	MemoryContext aggcontext;
 	bytea *sstate;
 	StringInfoData buf;
 	InternalCmpAggStore *result;
 	InternalCmpAggStoreIOState *my_extra;
 
-	if (!AggCheckCallContext(fcinfo, NULL))
+	if (!AggCheckCallContext(fcinfo, &aggcontext))
 		elog(ERROR, "aggregate function called in non-aggregate context");
 
 	sstate = PG_GETARG_BYTEA_P(0);
@@ -536,9 +539,9 @@ ts_bookend_deserializefunc(PG_FUNCTION_ARGS)
 		my_extra = (InternalCmpAggStoreIOState *) fcinfo->flinfo->fn_extra;
 	}
 
-	result = palloc(sizeof(InternalCmpAggStore));
-	polydatum_deserialize(&result->value, &buf, &my_extra->value, fcinfo);
-	polydatum_deserialize(&result->cmp, &buf, &my_extra->cmp, fcinfo);
+	result = MemoryContextAllocZero(aggcontext, sizeof(InternalCmpAggStore));
+	polydatum_deserialize(aggcontext, &result->value, &buf, &my_extra->value, fcinfo);
+	polydatum_deserialize(aggcontext, &result->cmp, &buf, &my_extra->cmp, fcinfo);
 	PG_RETURN_POINTER(result);
 }
 
diff --git a/test/expected/agg_bookends.out b/test/expected/agg_bookends.out
index 1c9868e146e..38811b89227 100644
--- a/test/expected/agg_bookends.out
+++ b/test/expected/agg_bookends.out
@@ -1500,3 +1500,42 @@ ROLLBACK;
  (1 row)
  
             time           | gp | temp 
+-- Test partial aggregation
+CREATE TABLE partial_aggregation (time timestamptz NOT NULL, quantity numeric, longvalue text);
+SELECT schema_name, table_name, created FROM create_hypertable('partial_aggregation', 'time');
+ schema_name |     table_name      | created 
+-------------+---------------------+---------
+ public      | partial_aggregation | t
+(1 row)
+
+INSERT INTO partial_aggregation VALUES('2018-01-20T09:00:43', NULL, NULL);
+INSERT INTO partial_aggregation VALUES('2018-01-20T09:00:43', NULL, NULL);
+INSERT INTO partial_aggregation VALUES('2019-01-20T09:00:43', 1, 'Hello');
+INSERT INTO partial_aggregation VALUES('2019-01-20T09:00:43', 2, 'World');
+-- Use enable_partitionwise_aggregate to create partial aggregates per chunk
+SET enable_partitionwise_aggregate = ON;
+SELECT first(time, quantity) FROM partial_aggregation;
+            first             
+------------------------------
+ Sun Jan 20 09:00:43 2019 PST
+(1 row)
+
+SELECT last(time, quantity) FROM partial_aggregation;
+             last             
+------------------------------
+ Sun Jan 20 09:00:43 2019 PST
+(1 row)
+
+SELECT first(longvalue, quantity) FROM partial_aggregation;
+ first 
+-------
+ Hello
+(1 row)
+
+SELECT last(longvalue, quantity) FROM partial_aggregation;
+ last  
+-------
+ World
+(1 row)
+
+SET enable_partitionwise_aggregate = OFF;
diff --git a/test/sql/agg_bookends.sql b/test/sql/agg_bookends.sql
index 3724874580f..a0ac7c4b576 100644
--- a/test/sql/agg_bookends.sql
+++ b/test/sql/agg_bookends.sql
@@ -31,3 +31,21 @@ SET timescaledb.enable_optimizations TO true;
 \o
 
 :DIFF_CMD
+
+-- Test partial aggregation
+CREATE TABLE partial_aggregation (time timestamptz NOT NULL, quantity numeric, longvalue text);
+SELECT schema_name, table_name, created FROM create_hypertable('partial_aggregation', 'time');
+
+INSERT INTO partial_aggregation VALUES('2018-01-20T09:00:43', NULL, NULL);
+INSERT INTO partial_aggregation VALUES('2018-01-20T09:00:43', NULL, NULL);
+INSERT INTO partial_aggregation VALUES('2019-01-20T09:00:43', 1, 'Hello');
+INSERT INTO partial_aggregation VALUES('2019-01-20T09:00:43', 2, 'World');
+
+-- Use enable_partitionwise_aggregate to create partial aggregates per chunk
+SET enable_partitionwise_aggregate = ON;
+SELECT first(time, quantity) FROM partial_aggregation;
+SELECT last(time, quantity) FROM partial_aggregation;
+SELECT first(longvalue, quantity) FROM partial_aggregation;
+SELECT last(longvalue, quantity) FROM partial_aggregation;
+SET enable_partitionwise_aggregate = OFF;
+