diff --git a/tpl/collections/collections.go b/tpl/collections/collections.go
index b025c7670..5d2cf3b35 100644
--- a/tpl/collections/collections.go
+++ b/tpl/collections/collections.go
@@ -545,7 +545,7 @@ func (ns *Namespace) Slice(args ...interface{}) []interface{} {
 // If either l1 or l2 is nil then the non-nil list will be returned.
 func (ns *Namespace) Union(l1, l2 interface{}) (interface{}, error) {
 	if l1 == nil && l2 == nil {
-		return nil, errors.New("both arrays/slices have to be of the same type")
+		return []interface{}{}, nil
 	} else if l1 == nil && l2 != nil {
 		return l2, nil
 	} else if l1 != nil && l2 == nil {
@@ -561,21 +561,96 @@ func (ns *Namespace) Union(l1, l2 interface{}) (interface{}, error) {
 		case reflect.Array, reflect.Slice:
 			r := reflect.MakeSlice(l1v.Type(), 0, 0)
 
-			if l1v.Type() != l2v.Type() {
+			if l1v.Type() != l2v.Type() &&
+				l1v.Type().Elem().Kind() != reflect.Interface &&
+				l2v.Type().Elem().Kind() != reflect.Interface {
+
 				return r.Interface(), nil
 			}
 
+			var l1vv reflect.Value
 			for i := 0; i < l1v.Len(); i++ {
-				elem := l1v.Index(i)
-				if !ns.In(r.Interface(), elem.Interface()) {
-					r = reflect.Append(r, elem)
+				l1vv = l1v.Index(i)
+				if !ns.In(r.Interface(), l1vv.Interface()) {
+					r = reflect.Append(r, l1vv)
 				}
 			}
 
 			for j := 0; j < l2v.Len(); j++ {
-				elem := l2v.Index(j)
-				if !ns.In(r.Interface(), elem.Interface()) {
-					r = reflect.Append(r, elem)
+				l2vv := l2v.Index(j)
+
+				switch l1vv.Kind() {
+				case reflect.String:
+					l2t, err := toString(l2vv)
+					if err == nil && !ns.In(r.Interface(), l2t) {
+						r = reflect.Append(r, reflect.ValueOf(l2t))
+					}
+				case reflect.Int:
+					l2t, err := toInt(l2vv)
+					if err == nil && !ns.In(r.Interface(), l2t) {
+						r = reflect.Append(r, reflect.ValueOf(int(l2t)))
+					}
+				case reflect.Int8:
+					l2t, err := toInt(l2vv)
+					if err == nil && !ns.In(r.Interface(), l2t) {
+						r = reflect.Append(r, reflect.ValueOf(int8(l2t)))
+					}
+				case reflect.Int16:
+					l2t, err := toInt(l2vv)
+					if err == nil && !ns.In(r.Interface(), l2t) {
+						r = reflect.Append(r, reflect.ValueOf(int16(l2t)))
+					}
+				case reflect.Int32:
+					l2t, err := toInt(l2vv)
+					if err == nil && !ns.In(r.Interface(), l2t) {
+						r = reflect.Append(r, reflect.ValueOf(int32(l2t)))
+					}
+				case reflect.Int64:
+					l2t, err := toInt(l2vv)
+					if err == nil && !ns.In(r.Interface(), l2t) {
+						r = reflect.Append(r, reflect.ValueOf(l2t))
+					}
+				case reflect.Float32:
+					l2t, err := toFloat(l2vv)
+					if err == nil && !ns.In(r.Interface(), float32(l2t)) {
+						r = reflect.Append(r, reflect.ValueOf(float32(l2t)))
+					}
+				case reflect.Float64:
+					l2t, err := toFloat(l2vv)
+					if err == nil && !ns.In(r.Interface(), l2t) {
+						r = reflect.Append(r, reflect.ValueOf(l2t))
+					}
+				case reflect.Interface:
+					switch l1vv.Interface().(type) {
+					case string:
+						switch l2vvActual := l2vv.Interface().(type) {
+						case string:
+							if !ns.In(r.Interface(), l2vvActual) {
+								r = reflect.Append(r, l2vv)
+							}
+						}
+					case int, int8, int16, int32, int64:
+						switch l2vvActual := l2vv.Interface().(type) {
+						case int, int8, int16, int32, int64:
+							if !ns.In(r.Interface(), l2vvActual) {
+								r = reflect.Append(r, l2vv)
+							}
+						}
+					case uint, uint8, uint16, uint32, uint64:
+						switch l2vvActual := l2vv.Interface().(type) {
+						case uint, uint8, uint16, uint32, uint64:
+							if !ns.In(r.Interface(), l2vvActual) {
+								r = reflect.Append(r, l2vv)
+							}
+						}
+					case float32, float64:
+						switch l2vvActual := l2vv.Interface().(type) {
+						case float32, float64:
+							if !ns.In(r.Interface(), l2vvActual) {
+								r = reflect.Append(r, l2vv)
+							}
+						}
+					}
 				}
 			}
 
diff --git a/tpl/collections/collections_test.go b/tpl/collections/collections_test.go
index 9943f439e..811cb4c87 100644
--- a/tpl/collections/collections_test.go
+++ b/tpl/collections/collections_test.go
@@ -571,21 +571,45 @@ func TestUnion(t *testing.T) {
 		expect interface{}
 		isErr  bool
 	}{
+		{nil, nil, []interface{}{}, false},
+		{nil, []string{"a", "b"}, []string{"a", "b"}, false},
+		{[]string{"a", "b"}, nil, []string{"a", "b"}, false},
+
+		// []A ∪ []B
+		{[]string{"1", "2"}, []int{3}, []string{}, false},
+		{[]int{1, 2}, []string{"1", "2"}, []int{}, false},
+
+		// []T ∪ []T
 		{[]string{"a", "b", "c", "c"}, []string{"a", "b", "b"}, []string{"a", "b", "c"}, false},
 		{[]string{"a", "b"}, []string{"a", "b", "c"}, []string{"a", "b", "c"}, false},
 		{[]string{"a", "b", "c"}, []string{"d", "e"}, []string{"a", "b", "c", "d", "e"}, false},
 		{[]string{}, []string{}, []string{}, false},
-		{[]string{"a", "b"}, nil, []string{"a", "b"}, false},
-		{nil, []string{"a", "b"}, []string{"a", "b"}, false},
-		{nil, nil, make([]interface{}, 0), true},
-		{[]string{"1", "2"}, []int{1, 2}, make([]string, 0), false},
-		{[]int{1, 2}, []string{"1", "2"}, make([]int, 0), false},
 		{[]int{1, 2, 3}, []int{3, 4, 5}, []int{1, 2, 3, 4, 5}, false},
 		{[]int{1, 2, 3}, []int{1, 2, 3}, []int{1, 2, 3}, false},
 		{[]int{1, 2, 4}, []int{2, 4}, []int{1, 2, 4}, false},
 		{[]int{2, 4}, []int{1, 2, 4}, []int{2, 4, 1}, false},
 		{[]int{1, 2, 4}, []int{3, 6}, []int{1, 2, 4, 3, 6}, false},
 		{[]float64{2.2, 4.4}, []float64{1.1, 2.2, 4.4}, []float64{2.2, 4.4, 1.1}, false},
+		{[]interface{}{"a", "b", "c", "c"}, []interface{}{"a", "b", "b"}, []interface{}{"a", "b", "c"}, false},
+
+		// []T ∪ []interface{}
+		{[]string{"1", "2"}, []interface{}{"9"}, []string{"1", "2", "9"}, false},
+		{[]int{2, 4}, []interface{}{1, 2, 4}, []int{2, 4, 1}, false},
+		{[]int8{2, 4}, []interface{}{int8(1), int8(2), int8(4)}, []int8{2, 4, 1}, false},
+		{[]int8{2, 4}, []interface{}{1, 2, 4}, []int8{2, 4, 1}, false},
+		{[]int16{2, 4}, []interface{}{1, 2, 4}, []int16{2, 4, 1}, false},
+		{[]int32{2, 4}, []interface{}{1, 2, 4}, []int32{2, 4, 1}, false},
+		{[]int64{2, 4}, []interface{}{1, 2, 4}, []int64{2, 4, 1}, false},
+		{[]float64{2.2, 4.4}, []interface{}{1.1, 2.2, 4.4}, []float64{2.2, 4.4, 1.1}, false},
+		{[]float32{2.2, 4.4}, []interface{}{1.1, 2.2, 4.4}, []float32{2.2, 4.4, 1.1}, false},
+
+		// []interface{} ∪ []T
+		{[]interface{}{"a", "b", "c", "c"}, []string{"a", "b", "b"}, []interface{}{"a", "b", "c"}, false},
+		{[]interface{}{}, []string{}, []interface{}{}, false},
+		{[]interface{}{1, 2}, []int{2, 3}, []interface{}{1, 2, 3}, false},
+		{[]interface{}{1, 2}, []int8{2, 3}, []interface{}{1, 2, int8(3)}, false},
+		{[]interface{}{1.1, 2.2}, []float64{2.2, 3.3}, []interface{}{1.1, 2.2, 3.3}, false},
+
 		// errors
 		{"not array or slice", []string{"a"}, false, true},
 		{[]string{"a"}, "not array or slice", false, true},