diff --git a/src/backend/utils/adt/numeric.c b/src/backend/utils/adt/numeric.c
index 229b408..6e1a6ae 100644
--- a/src/backend/utils/adt/numeric.c
+++ b/src/backend/utils/adt/numeric.c
@@ -259,6 +259,13 @@ typedef struct NumericVar
 	NumericDigit *digits;		/* base-NBASE digits */
 } NumericVar;
 
+/* Transition state for numeric average aggregate. */
+typedef struct AvgAggState
+{
+	Numeric 	sumX;
+	uint64 		N;
+	size_t 		sumX_size;
+} AvgAggState;
 
 /* ----------
  * Some preinitialized constants
@@ -432,7 +439,7 @@ static void trunc_var(NumericVar *var, int rscale);
 static void strip_var(NumericVar *var);
 static void compute_bucket(Numeric operand, Numeric bound1, Numeric bound2,
 			   NumericVar *count_var, NumericVar *result_var);
-
+static AvgAggState * makeAvgAggState(FunctionCallInfo fcinfo);
 
 /* ----------------------------------------------------------------------
  *
@@ -2511,38 +2518,28 @@ do_numeric_accum(ArrayType *transarray, Numeric newval)
 	return result;
 }
 
-/*
- * Improve avg performance by not caclulating sum(X*X).
- */
-static ArrayType *
-do_numeric_avg_accum(ArrayType *transarray, Numeric newval)
+static void
+do_numeric_avg_accum(AvgAggState *state, Numeric newval)
 {
-	Datum	   *transdatums;
-	int			ndatums;
-	Datum		N,
-				sumX;
-	ArrayType  *result;
+	Numeric 	 newsumX;
+	size_t		 newsumX_size;
 
-	/* We assume the input is array of numeric */
-	deconstruct_array(transarray,
-					  NUMERICOID, -1, false, 'i',
-					  &transdatums, NULL, &ndatums);
-	if (ndatums != 2)
-		elog(ERROR, "expected 2-element numeric array");
-	N = transdatums[0];
-	sumX = transdatums[1];
+	/* Calculate the new value for sumX. */
+	newsumX = DatumGetNumeric(DirectFunctionCall2(numeric_add, 
+							  NumericGetDatum(state->sumX),
+							  NumericGetDatum(newval)));
 
-	N = DirectFunctionCall1(numeric_inc, N);
-	sumX = DirectFunctionCall2(numeric_add, sumX,
-							   NumericGetDatum(newval));
-
-	transdatums[0] = N;
-	transdatums[1] = sumX;
-
-	result = construct_array(transdatums, 2,
-							 NUMERICOID, -1, false, 'i');
+	/* Enlarge state->sumX to have enough space for the new sumX. */
+	newsumX_size = VARSIZE(newsumX);
+	if (newsumX_size > state->sumX_size)
+	{
+		state->sumX = repalloc(state->sumX, newsumX_size);
+		state->sumX_size = newsumX_size;
+	}
 
-	return result;
+	/* Update state. */
+	memcpy(state->sumX, newsumX, newsumX_size);
+	state->N++;
 }
 
 Datum
@@ -2560,10 +2557,20 @@ numeric_accum(PG_FUNCTION_ARGS)
 Datum
 numeric_avg_accum(PG_FUNCTION_ARGS)
 {
-	ArrayType  *transarray = PG_GETARG_ARRAYTYPE_P(0);
-	Numeric		newval = PG_GETARG_NUMERIC(1);
+	AvgAggState *state;
+
+	state = PG_ARGISNULL(0) ? NULL : (AvgAggState *) PG_GETARG_POINTER(0);
+
+	if (!PG_ARGISNULL(1))
+	{
+		/* On the first time through, create the state variable. */
+		if (state == NULL)
+			state = makeAvgAggState(fcinfo);
+		
+		do_numeric_avg_accum(state, PG_GETARG_NUMERIC(1));
+	}
 
-	PG_RETURN_ARRAYTYPE_P(do_numeric_avg_accum(transarray, newval));
+	PG_RETURN_POINTER(state);
 }
 
 /*
@@ -2617,42 +2624,43 @@ int8_accum(PG_FUNCTION_ARGS)
 Datum
 int8_avg_accum(PG_FUNCTION_ARGS)
 {
-	ArrayType  *transarray = PG_GETARG_ARRAYTYPE_P(0);
-	Datum		newval8 = PG_GETARG_DATUM(1);
-	Numeric		newval;
+	AvgAggState *state;
 
-	newval = DatumGetNumeric(DirectFunctionCall1(int8_numeric, newval8));
+	state = PG_ARGISNULL(0) ? NULL : (AvgAggState *) PG_GETARG_POINTER(0);
 
-	PG_RETURN_ARRAYTYPE_P(do_numeric_avg_accum(transarray, newval));
-}
+	if (!PG_ARGISNULL(1))
+	{
+		Datum		newval8;
+		Numeric		newval;
 
+		/* On the first time through, create the state variable. */
+		if (state == NULL)
+			state = makeAvgAggState(fcinfo);
+
+		newval8 = PG_GETARG_DATUM(1);
+		newval = DatumGetNumeric(DirectFunctionCall1(int8_numeric, newval8));
+		
+		do_numeric_avg_accum(state, newval);
+	}
+
+	PG_RETURN_POINTER(state);
+}
 
 Datum
 numeric_avg(PG_FUNCTION_ARGS)
 {
-	ArrayType  *transarray = PG_GETARG_ARRAYTYPE_P(0);
-	Datum	   *transdatums;
-	int			ndatums;
-	Numeric		N,
-				sumX;
+	Datum 		 countd;
+	AvgAggState *state;
 
-	/* We assume the input is array of numeric */
-	deconstruct_array(transarray,
-					  NUMERICOID, -1, false, 'i',
-					  &transdatums, NULL, &ndatums);
-	if (ndatums != 2)
-		elog(ERROR, "expected 2-element numeric array");
-	N = DatumGetNumeric(transdatums[0]);
-	sumX = DatumGetNumeric(transdatums[1]);
-
-	/* SQL92 defines AVG of no values to be NULL */
-	/* N is zero iff no digits (cf. numeric_uminus) */
-	if (NUMERIC_NDIGITS(N) == 0)
+	if (PG_ARGISNULL(0))
 		PG_RETURN_NULL();
 
+	state = (AvgAggState *) PG_GETARG_POINTER(0);
+	countd = DirectFunctionCall1(int8_numeric, Int64GetDatum(state->N));
+
 	PG_RETURN_DATUM(DirectFunctionCall2(numeric_div,
-										NumericGetDatum(sumX),
-										NumericGetDatum(N)));
+										NumericGetDatum(state->sumX),
+										countd));
 }
 
 /*
@@ -6170,3 +6178,39 @@ strip_var(NumericVar *var)
 	var->digits = digits;
 	var->ndigits = ndigits;
 }
+
+/*
+ * makeAvgAggState
+ *
+ * Initialize state for numeric avg aggregate in the aggregate context
+ */
+static AvgAggState * 
+makeAvgAggState(FunctionCallInfo fcinfo)
+{
+	AvgAggState 	*state;
+	NumericVar 		*sumX_var;
+	MemoryContext 	 agg_context;
+	MemoryContext 	 old_context;
+
+	if (!AggCheckCallContext(fcinfo, &agg_context))
+	{
+		/* cannot be called directly because of internal-type argument */
+		elog(ERROR, "numeric_avg_accum called in non-aggregate context");
+	}
+
+	sumX_var = palloc0(sizeof(NumericVar));
+	zero_var(sumX_var);
+
+	/*
+	 * Create state in aggregate context.  It'll stay there across subsequent
+	 * calls.
+	 */
+	old_context = MemoryContextSwitchTo(agg_context);
+	state = palloc0(sizeof(AvgAggState));
+	state->sumX = make_result(sumX_var);
+	state->sumX_size = VARSIZE(state->sumX);
+	state->N = 0;
+	MemoryContextSwitchTo(old_context);
+
+	return state;
+}
diff --git a/src/include/catalog/pg_aggregate.h b/src/include/catalog/pg_aggregate.h
index 6fb10a9..b34fedf 100644
--- a/src/include/catalog/pg_aggregate.h
+++ b/src/include/catalog/pg_aggregate.h
@@ -77,10 +77,10 @@ typedef FormData_pg_aggregate *Form_pg_aggregate;
  */
 
 /* avg */
-DATA(insert ( 2100	int8_avg_accum	numeric_avg		0	1231	"{0,0}" ));
+DATA(insert ( 2100	int8_avg_accum	numeric_avg		0	2281	_null_ ));
 DATA(insert ( 2101	int4_avg_accum	int8_avg		0	1016	"{0,0}" ));
 DATA(insert ( 2102	int2_avg_accum	int8_avg		0	1016	"{0,0}" ));
-DATA(insert ( 2103	numeric_avg_accum	numeric_avg		0	1231	"{0,0}" ));
+DATA(insert ( 2103	numeric_avg_accum	numeric_avg		0	2281	_null_ ));
 DATA(insert ( 2104	float4_accum	float8_avg		0	1022	"{0,0,0}" ));
 DATA(insert ( 2105	float8_accum	float8_avg		0	1022	"{0,0,0}" ));
 DATA(insert ( 2106	interval_accum	interval_avg	0	1187	"{0 second,0 second}" ));
diff --git a/src/include/catalog/pg_proc.h b/src/include/catalog/pg_proc.h
index c97056e..f30a7a3 100644
--- a/src/include/catalog/pg_proc.h
+++ b/src/include/catalog/pg_proc.h
@@ -2385,7 +2385,7 @@ DATA(insert OID = 1832 (  float8_stddev_samp	PGNSP PGUID 12 1 0 0 0 f f f f t f
 DESCR("aggregate final function");
 DATA(insert OID = 1833 (  numeric_accum    PGNSP PGUID 12 1 0 0 0 f f f f t f i 2 0 1231 "1231 1700" _null_ _null_ _null_ _null_ numeric_accum _null_ _null_ _null_ ));
 DESCR("aggregate transition function");
-DATA(insert OID = 2858 (  numeric_avg_accum    PGNSP PGUID 12 1 0 0 0 f f f f t f i 2 0 1231 "1231 1700" _null_ _null_ _null_ _null_ numeric_avg_accum _null_ _null_ _null_ ));
+DATA(insert OID = 2858 (  numeric_avg_accum    PGNSP PGUID 12 1 0 0 0 f f f f f f i 2 0 2281 "2281 1700" _null_ _null_ _null_ _null_ numeric_avg_accum _null_ _null_ _null_ ));
 DESCR("aggregate transition function");
 DATA(insert OID = 1834 (  int2_accum	   PGNSP PGUID 12 1 0 0 0 f f f f t f i 2 0 1231 "1231 21" _null_ _null_ _null_ _null_ int2_accum _null_ _null_ _null_ ));
 DESCR("aggregate transition function");
@@ -2393,9 +2393,9 @@ DATA(insert OID = 1835 (  int4_accum	   PGNSP PGUID 12 1 0 0 0 f f f f t f i 2 0
 DESCR("aggregate transition function");
 DATA(insert OID = 1836 (  int8_accum	   PGNSP PGUID 12 1 0 0 0 f f f f t f i 2 0 1231 "1231 20" _null_ _null_ _null_ _null_ int8_accum _null_ _null_ _null_ ));
 DESCR("aggregate transition function");
-DATA(insert OID = 2746 (  int8_avg_accum	   PGNSP PGUID 12 1 0 0 0 f f f f t f i 2 0 1231 "1231 20" _null_ _null_ _null_ _null_ int8_avg_accum _null_ _null_ _null_ ));
+DATA(insert OID = 2746 (  int8_avg_accum	   PGNSP PGUID 12 1 0 0 0 f f f f f f i 2 0 2281 "2281 20" _null_ _null_ _null_ _null_ int8_avg_accum _null_ _null_ _null_ ));
 DESCR("aggregate transition function");
-DATA(insert OID = 1837 (  numeric_avg	   PGNSP PGUID 12 1 0 0 0 f f f f t f i 1 0 1700 "1231" _null_ _null_ _null_ _null_ numeric_avg _null_ _null_ _null_ ));
+DATA(insert OID = 1837 (  numeric_avg	   PGNSP PGUID 12 1 0 0 0 f f f f f f i 1 0 1700 "2281" _null_ _null_ _null_ _null_ numeric_avg _null_ _null_ _null_ ));
 DESCR("aggregate final function");
 DATA(insert OID = 2514 (  numeric_var_pop  PGNSP PGUID 12 1 0 0 0 f f f f t f i 1 0 1700 "1231" _null_ _null_ _null_ _null_ numeric_var_pop _null_ _null_ _null_ ));
 DESCR("aggregate final function");