diff --git a/core/mapping/unmarshaler.go b/core/mapping/unmarshaler.go
index 780b2420..a8be682c 100644
--- a/core/mapping/unmarshaler.go
+++ b/core/mapping/unmarshaler.go
@@ -448,10 +448,12 @@ func (u *Unmarshaler) fillSlice(fieldType reflect.Type, value reflect.Value, map
 	dereffedBaseType := Deref(baseType)
 	dereffedBaseKind := dereffedBaseType.Kind()
 	refValue := reflect.ValueOf(mapValue)
-	conv := reflect.MakeSlice(reflect.SliceOf(baseType), refValue.Len(), refValue.Cap())
+	if refValue.IsNil() {
+		return nil
+	}
 
-	// support for empty slice
-	if !refValue.IsNil() && refValue.Len() == 0 {
+	conv := reflect.MakeSlice(reflect.SliceOf(baseType), refValue.Len(), refValue.Cap())
+	if refValue.Len() == 0 {
 		value.Set(conv)
 		return nil
 	}
diff --git a/core/mapping/unmarshaler_test.go b/core/mapping/unmarshaler_test.go
index e71adca2..1b3bdcfc 100644
--- a/core/mapping/unmarshaler_test.go
+++ b/core/mapping/unmarshaler_test.go
@@ -198,6 +198,49 @@ func TestUnmarshalIntWithDefault(t *testing.T) {
 	assert.Equal(t, 1, in.Int)
 }
 
+func TestUnmarshalBoolSliceRequired(t *testing.T) {
+	type inner struct {
+		Bools []bool `key:"bools"`
+	}
+
+	var in inner
+	assert.NotNil(t, UnmarshalKey(map[string]interface{}{}, &in))
+}
+
+func TestUnmarshalBoolSliceNil(t *testing.T) {
+	type inner struct {
+		Bools []bool `key:"bools,optional"`
+	}
+
+	var in inner
+	assert.Nil(t, UnmarshalKey(map[string]interface{}{}, &in))
+	assert.Nil(t, in.Bools)
+}
+
+func TestUnmarshalBoolSliceNilExplicit(t *testing.T) {
+	type inner struct {
+		Bools []bool `key:"bools,optional"`
+	}
+
+	var in inner
+	assert.Nil(t, UnmarshalKey(map[string]interface{}{
+		"bools": nil,
+	}, &in))
+	assert.Nil(t, in.Bools)
+}
+
+func TestUnmarshalBoolSliceEmpty(t *testing.T) {
+	type inner struct {
+		Bools []bool `key:"bools,optional"`
+	}
+
+	var in inner
+	assert.Nil(t, UnmarshalKey(map[string]interface{}{
+		"bools": []bool{},
+	}, &in))
+	assert.Empty(t, in.Bools)
+}
+
 func TestUnmarshalBoolSliceWithDefault(t *testing.T) {
 	type inner struct {
 		Bools []bool `key:"bools,default=[true,false]"`