diff --git a/storage/filesystem.go b/storage/filesystem.go
index 53f3882..ee46863 100644
--- a/storage/filesystem.go
+++ b/storage/filesystem.go
@@ -249,7 +249,7 @@ func (b *filesystemBackend) AddressBook(ctx context.Context) (*carddav.AddressBo
 		data, readErr = ioutil.ReadFile(path)
 	}
 	if readErr != nil {
-		return nil, fmt.Errorf("error opening address book: %s", err.Error())
+		return nil, fmt.Errorf("error opening address book: %s", readErr.Error())
 	}
 	var addressBook carddav.AddressBook
 	err = json.Unmarshal(data, &addressBook)
@@ -493,7 +493,7 @@ func (b *filesystemBackend) Calendar(ctx context.Context) (*caldav.Calendar, err
 	debug.Printf("loading calendar from %s", path)
 
 	data, readErr := ioutil.ReadFile(path)
-	if os.IsNotExist(err) {
+	if os.IsNotExist(readErr) {
 		homeSetPath, err := b.CalendarHomeSetPath(ctx)
 		if err != nil {
 			return nil, err
@@ -506,7 +506,7 @@ func (b *filesystemBackend) Calendar(ctx context.Context) (*caldav.Calendar, err
 		data, readErr = ioutil.ReadFile(path)
 	}
 	if readErr != nil {
-		return nil, fmt.Errorf("error opening calendar: %s", err.Error())
+		return nil, fmt.Errorf("error opening calendar: %s", readErr.Error())
 	}
 	var calendar caldav.Calendar
 	err = json.Unmarshal(data, &calendar)