diff --git a/pkg/files/filehandling.go b/pkg/files/filehandling.go
index c0c3dcfcd..d2acb8278 100644
--- a/pkg/files/filehandling.go
+++ b/pkg/files/filehandling.go
@@ -17,12 +17,14 @@
 package files
 
 import (
+	"bytes"
 	"errors"
 	"fmt"
 	"os"
 	"path/filepath"
 	"strings"
 	"testing"
+	"time"
 
 	"code.vikunja.io/api/pkg/config"
 	"code.vikunja.io/api/pkg/db"
@@ -107,6 +109,7 @@ func initS3FileHandler() error {
 func initLocalFileHandler() {
 	fs = afero.NewOsFs()
 	afs = &afero.Afero{Fs: fs}
+	s3Client = nil
 	setDefaultLocalConfig()
 }
 
@@ -116,13 +119,20 @@ func InitFileHandler() error {
 
 	switch fileType {
 	case "s3":
-		return initS3FileHandler()
+		if err := initS3FileHandler(); err != nil {
+			return err
+		}
 	case "local":
 		initLocalFileHandler()
-		return nil
 	default:
 		return fmt.Errorf("invalid file storage type '%s': must be 'local' or 's3'", fileType)
 	}
+
+	if err := ValidateFileStorage(); err != nil {
+		return fmt.Errorf("storage validation failed: %w", err)
+	}
+
+	return nil
 }
 
 // InitTestFileHandler initializes a new memory file system for testing
@@ -175,3 +185,22 @@ func InitTests() {
 func FileStat(file *File) (os.FileInfo, error) {
 	return afs.Stat(file.getAbsoluteFilePath())
 }
+
+// ValidateFileStorage checks that the configured file storage is writable
+// by creating and removing a temporary file.
+func ValidateFileStorage() error {
+	filename := fmt.Sprintf(".vikunja-check-%d", time.Now().UnixNano())
+	path := filepath.Join(config.FilesBasePath.GetString(), filename)
+
+	err := writeToStorage(path, bytes.NewReader([]byte{}), 0)
+	if err != nil {
+		return fmt.Errorf("failed to create test file at %s: %w", path, err)
+	}
+
+	err = afs.Remove(path)
+	if err != nil {
+		return fmt.Errorf("failed to remove test file at %s: %w", path, err)
+	}
+
+	return nil
+}
diff --git a/pkg/files/files.go b/pkg/files/files.go
index 2f25a6c83..01b5cfd16 100644
--- a/pkg/files/files.go
+++ b/pkg/files/files.go
@@ -152,22 +152,13 @@ func (f *File) Delete(s *xorm.Session) (err error) {
 	return keyvalue.DecrBy(metrics.FilesCountKey, 1)
 }
 
-// Save saves a file to storage
-func (f *File) Save(fcontent io.Reader) (err error) {
-
+// writeToStorage writes content to the given path, handling both local and S3 backends
+func writeToStorage(path string, content io.Reader, size uint64) error {
 	if s3Client == nil {
-		err = afs.WriteReader(f.getAbsoluteFilePath(), fcontent)
-		if err != nil {
-			return fmt.Errorf("failed to save file: %w", err)
-		}
-
-		return keyvalue.IncrBy(metrics.FilesCountKey, 1)
+		return afs.WriteReader(path, content)
 	}
 
-	// For S3 storage, use PutObject directly with Content-Length to enable streaming
-	// without buffering the entire file in memory. Some S3-compatible services
-	// (like MinIO) require Content-Length to be set explicitly.
-	body, contentLength, cleanup, err := prepareS3UploadBody(fcontent, f.Size)
+	body, contentLength, cleanup, err := prepareS3UploadBody(content, size)
 	if err != nil {
 		return err
 	}
@@ -177,14 +168,22 @@ func (f *File) Save(fcontent io.Reader) (err error) {
 
 	_, err = s3Client.PutObject(&s3.PutObjectInput{
 		Bucket:        aws.String(s3Bucket),
-		Key:           aws.String(f.getAbsoluteFilePath()),
+		Key:           aws.String(path),
 		Body:          body,
 		ContentLength: aws.Int64(contentLength),
 	})
 	if err != nil {
 		return fmt.Errorf("failed to upload file to S3: %w", err)
 	}
+	return nil
+}
 
+// Save saves a file to storage
+func (f *File) Save(fcontent io.Reader) error {
+	err := writeToStorage(f.getAbsoluteFilePath(), fcontent, f.Size)
+	if err != nil {
+		return fmt.Errorf("failed to save file: %w", err)
+	}
 	return keyvalue.IncrBy(metrics.FilesCountKey, 1)
 }
 
diff --git a/pkg/files/s3_test.go b/pkg/files/s3_test.go
index badcde106..1f2ef5a72 100644
--- a/pkg/files/s3_test.go
+++ b/pkg/files/s3_test.go
@@ -220,9 +220,12 @@ func TestInitFileHandler_S3Configuration(t *testing.T) {
 		config.FilesS3AccessKey.Set("test-access-key")
 		config.FilesS3SecretKey.Set("test-secret-key")
 
-		// This should not return an error with valid configuration
+		// With valid configuration, InitFileHandler will succeed at config parsing
+		// but fail at storage validation (since the S3 endpoint isn't real).
+		// The error should be from validation, not from config parsing.
 		err := InitFileHandler()
-		assert.NoError(t, err)
+		require.Error(t, err)
+		assert.Contains(t, err.Error(), "storage validation failed")
 	})
 
 	t.Run("missing S3 endpoint", func(t *testing.T) {
@@ -281,14 +284,20 @@ func TestInitFileHandler_S3Configuration(t *testing.T) {
 func TestInitFileHandler_LocalFilesystem(t *testing.T) {
 	// Save original config values
 	originalType := config.FilesType.GetString()
+	originalBasePath := config.FilesBasePath.GetString()
+
+	// Create a temp directory for the test
+	tempDir := t.TempDir()
 
 	// Restore config after test
 	defer func() {
 		config.FilesType.Set(originalType)
+		config.FilesBasePath.Set(originalBasePath)
 	}()
 
-	// Test with local filesystem
+	// Test with local filesystem using writable temp directory
 	config.FilesType.Set("local")
+	config.FilesBasePath.Set(tempDir)
 
 	// This should not return an error
 	err := InitFileHandler()