diff --git a/group_private.go b/group_private.go
index 3ce957b..5242f5d 100644
--- a/group_private.go
+++ b/group_private.go
@@ -17,12 +17,6 @@
 	}
 }
 
-func (g *Group) clear() {
-	for _, option := range g.options {
-		option.clear()
-	}
-}
-
 func (g *Group) optionByName(name string, namematch func(*Option, string) bool) *Option {
 	prio := 0
 	var retopt *Option
diff --git a/parser.go b/parser.go
index 2c1e98f..4662200 100644
--- a/parser.go
+++ b/parser.go
@@ -131,7 +131,13 @@
 	p.eachCommand(func(c *Command) {
 		c.eachGroup(func(g *Group) {
 			g.storeDefaults()
-			g.clear()
+
+			for _, option := range g.options {
+				switch option.value.Type().Kind() {
+				case reflect.Func, reflect.Map, reflect.Slice:
+					option.clear()
+				}
+			}
 		})
 	}, true)
 
@@ -203,15 +209,13 @@
 					tp := option.value.Type()
 
 					switch tp.Kind() {
-					case reflect.Func:
-						// Skip
 					case reflect.Map:
 						if option.value.Len() == 0 {
 							for _, k := range option.defaultValue.MapKeys() {
 								option.value.SetMapIndex(k, option.defaultValue.MapIndex(k))
 							}
 						}
-					default:
+					case reflect.Slice:
 						if reflect.DeepEqual(option.value.Interface(), reflect.Zero(tp).Interface()) {
 							option.value.Set(option.defaultValue)
 						}
diff --git a/parser_test.go b/parser_test.go
new file mode 100644
index 0000000..b227244
--- /dev/null
+++ b/parser_test.go
@@ -0,0 +1,98 @@
+package flags
+
+import (
+	"reflect"
+	"testing"
+	"time"
+)
+
+type defaultOptions struct {
+	Int        int `long:"i"`
+	IntDefault int `long:"id" default:"1"`
+
+	Time        time.Duration `long:"t"`
+	TimeDefault time.Duration `long:"td" default:"1m"`
+
+	Map        map[string]int `long:"m"`
+	MapDefault map[string]int `long:"md" default:"a:1"`
+
+	Slice        []int `long:"s"`
+	SliceDefault []int `long:"sd" default:"1" default:"2"`
+}
+
+func TestDefaults(t *testing.T) {
+	var tests = []struct {
+		msg      string
+		args     []string
+		expected defaultOptions
+	}{
+		{
+			msg:  "no arguments, expecting default values",
+			args: []string{},
+			expected: defaultOptions{
+				Int:        0,
+				IntDefault: 1,
+
+				Time:        0,
+				TimeDefault: time.Minute,
+
+				Map:        map[string]int{},
+				MapDefault: map[string]int{"a": 1},
+
+				Slice:        []int{},
+				SliceDefault: []int{1, 2},
+			},
+		},
+		{
+			msg:  "non-zero value arguments, expecting overwritten arguments",
+			args: []string{"--i=3", "--id=3", "--t=3ms", "--td=3ms", "--m=c:3", "--md=c:3", "--s=3", "--sd=3"},
+			expected: defaultOptions{
+				Int:        3,
+				IntDefault: 3,
+
+				Time:        3 * time.Millisecond,
+				TimeDefault: 3 * time.Millisecond,
+
+				Map:        map[string]int{"c": 3},
+				MapDefault: map[string]int{"c": 3},
+
+				Slice:        []int{3},
+				SliceDefault: []int{3},
+			},
+		},
+		{
+			msg:  "zero value arguments, expecting overwritten arguments",
+			args: []string{"--i=0", "--id=0", "--t=0ms", "--td=0s", "--m=:0", "--md=:0", "--s=0", "--sd=0"},
+			expected: defaultOptions{
+				Int:        0,
+				IntDefault: 0,
+
+				Time:        0,
+				TimeDefault: 0,
+
+				Map:        map[string]int{"": 0},
+				MapDefault: map[string]int{"": 0},
+
+				Slice:        []int{0},
+				SliceDefault: []int{0},
+			},
+		},
+	}
+
+	for _, test := range tests {
+		var opts defaultOptions
+
+		_, err := ParseArgs(&opts, test.args)
+		if err != nil {
+			t.Fatalf("%s:\nUnexpected error: %v", test.msg, err)
+		}
+
+		if opts.Slice == nil {
+			opts.Slice = []int{}
+		}
+
+		if !reflect.DeepEqual(opts, test.expected) {
+			t.Errorf("%s:\nUnexpected options with arguments %+v\nexpected\n%+v\nbut got\n%+v\n", test.msg, test.args, test.expected, opts)
+		}
+	}
+}