diff --git a/src/423groupby.js b/src/423groupby.js
index 39461210fe..3dd2c9034c 100755
--- a/src/423groupby.js
+++ b/src/423groupby.js
@@ -51,7 +51,7 @@ yy.Select.prototype.compileGroup = function (query) {
 
 	query.ingroup = [];
 	var s = '';
-	allgroup.forEach(function (agroup) {
+	allgroup.forEach(function (agroup, setIdx) {
 		// Start of group function
 		s += 'var g=this.xgroups[';
 
@@ -71,9 +71,16 @@ yy.Select.prototype.compileGroup = function (query) {
 			rg = ["''"];
 		}
 
-		s += rg.join('+"`"+');
+		// With several grouping sets (CUBE, ROLLUP, GROUPING SETS) the same values can
+		// appear in different sets, e.g. (a=2) and (b=2), so the key must include the set
+		var groupKey = rg.join('+"`"+');
+		if (allgroup.length > 1) {
+			groupKey = `'${setIdx}\`'+` + groupKey;
+		}
+
+		s += groupKey;
 		s += '];if(!g) {this.groups.push((g=this.xgroups[';
-		s += rg.join('+"`"+');
+		s += groupKey;
 		s += '] = {';
 		s += agroup
 			.map(function (col2) {
diff --git a/test/test015.js b/test/test015.js
index ba5ab60b2b..2546068a1b 100644
--- a/test/test015.js
+++ b/test/test015.js
@@ -21,15 +21,21 @@ describe('Test 15', function () {
 			'SELECT a,b,c, SUM(d) AS d FROM test ' + ' GROUP BY GROUPING SETS(a,b),c ORDER BY a,b,c'
 		);
 
+		// Grouping sets (a,c) and (b,c) are separate groups (see #644)
 		var tobe = [
-			{a: 0, b: null, c: 0, d: 1000},
-			{a: 0, b: null, c: 1, d: 1400},
-			{a: null, b: 1, c: 0, d: 2200},
-			{a: null, b: 1, c: 1, d: 2600},
+			{a: 0, b: null, c: 0, d: 400},
+			{a: null, b: 0, c: 0, d: 600},
+			{a: 0, b: null, c: 1, d: 600},
+			{a: null, b: 0, c: 1, d: 800},
+			{a: null, b: 1, c: 0, d: 1000},
+			{a: null, b: 1, c: 1, d: 1200},
+			{a: 1, b: null, c: 0, d: 1200},
+			{a: 1, b: null, c: 1, d: 1400},
 		];
 
+		assert.equal(res.length, tobe.length);
 		var check = true;
-		for (var i = 0; i < 4; i++) {
+		for (var i = 0; i < tobe.length; i++) {
 			for (var p in tobe[i]) {
 				check = check && res[i][p] == tobe[i][p];
 			}
diff --git a/test/test644.js b/test/test644.js
new file mode 100644
index 0000000000..1815ace73a
--- /dev/null
+++ b/test/test644.js
@@ -0,0 +1,69 @@
+if (typeof exports === 'object') {
+	var assert = require('assert');
+	var alasql = require('..');
+}
+
+let testId = '644'; // GROUP BY CUBE / GROUPING SETS merged groups from different grouping sets
+
+describe(`Test ${testId} - CUBE and GROUPING SETS keep grouping sets apart`, function () {
+	const data = [
+		{a: 2, b: 2, v: 15},
+		{a: 2, b: 4, v: 20},
+	];
+
+	it('A) CUBE(a, b) from the issue', function () {
+		const res = alasql('SELECT a, b, SUM(v) AS s FROM ? GROUP BY CUBE(a, b)', [data]);
+		assert.deepStrictEqual(res, [
+			{a: null, b: null, s: 35},
+			{a: 2, b: null, s: 35},
+			{a: null, b: 2, s: 15},
+			{a: 2, b: 2, s: 15},
+			{a: null, b: 4, s: 20},
+			{a: 2, b: 4, s: 20},
+		]);
+	});
+
+	it('B) GROUPING SETS(a, b) with overlapping values', function () {
+		const res = alasql('SELECT a, b, SUM(v) AS s FROM ? GROUP BY GROUPING SETS(a, b)', [data]);
+		assert.deepStrictEqual(res, [
+			{a: 2, b: null, s: 35},
+			{a: null, b: 2, s: 15},
+			{a: null, b: 4, s: 20},
+		]);
+	});
+
+	it('C) CUBE with COUNT over several rows', function () {
+		const rows = [
+			{x: 'p', y: 'p'},
+			{x: 'p', y: 'q'},
+			{x: 'q', y: 'p'},
+		];
+		const res = alasql('SELECT x, y, COUNT(*) AS c FROM ? GROUP BY CUBE(x, y)', [rows]);
+		assert.deepStrictEqual(res, [
+			{x: null, y: null, c: 3},
+			{x: 'p', y: null, c: 2},
+			{x: null, y: 'p', c: 2},
+			{x: 'p', y: 'p', c: 1},
+			{x: null, y: 'q', c: 1},
+			{x: 'p', y: 'q', c: 1},
+			{x: 'q', y: null, c: 1},
+			{x: 'q', y: 'p', c: 1},
+		]);
+	});
+
+	it('D) ROLLUP and plain GROUP BY are unchanged', function () {
+		assert.deepStrictEqual(
+			alasql('SELECT a, b, SUM(v) AS s FROM ? GROUP BY ROLLUP(a, b)', [data]),
+			[
+				{a: null, b: null, s: 35},
+				{a: 2, b: null, s: 35},
+				{a: 2, b: 2, s: 15},
+				{a: 2, b: 4, s: 20},
+			]
+		);
+		assert.deepStrictEqual(alasql('SELECT a, b, SUM(v) AS s FROM ? GROUP BY a, b', [data]), [
+			{a: 2, b: 2, s: 15},
+			{a: 2, b: 4, s: 20},
+		]);
+	});
+});