diff --git a/config-raw.json b/config-raw.json
index 4df3590d4..8e1e7d686 100644
--- a/config-raw.json
+++ b/config-raw.json
@@ -528,6 +528,11 @@
                             "key": "usepathstyle",
                             "default_value": "false",
                             "comment": "Whether to use path-style addressing (e.g., https://s3.amazonaws.com/bucket/key) instead of virtual-hosted-style (e.g., https://bucket.s3.amazonaws.com/key). This is commonly needed for self-hosted S3-compatible services. Some providers only support one style or the other."
+                        },
+                        {
+                            "key": "disablesigning",
+                            "default_value": "false",
+                            "comment": "When enabled, the S3 client will send UNSIGNED-PAYLOAD instead of computing a SHA256 hash for request signing. Some S3-compatible providers (such as Ceph RadosGW, Clever Cloud Cellar) do not correctly verify payload signatures and return XAmzContentSHA256Mismatch errors. Enabling this option works around the issue. Only applies over HTTPS."
                         }
                     ]
                 }
diff --git a/pkg/config/config.go b/pkg/config/config.go
index 64e931893..b8d56e9ad 100644
--- a/pkg/config/config.go
+++ b/pkg/config/config.go
@@ -162,13 +162,14 @@ const (
 	FilesType     Key = `files.type`
 
 	// S3 Configuration
-	FilesS3Endpoint     Key = `files.s3.endpoint`
-	FilesS3Bucket       Key = `files.s3.bucket`
-	FilesS3Region       Key = `files.s3.region`
-	FilesS3AccessKey    Key = `files.s3.accesskey`
-	FilesS3SecretKey    Key = `files.s3.secretkey`
-	FilesS3UsePathStyle Key = `files.s3.usepathstyle`
-	FilesS3TempDir      Key = `files.s3.tempdir`
+	FilesS3Endpoint       Key = `files.s3.endpoint`
+	FilesS3Bucket         Key = `files.s3.bucket`
+	FilesS3Region         Key = `files.s3.region`
+	FilesS3AccessKey      Key = `files.s3.accesskey`
+	FilesS3SecretKey      Key = `files.s3.secretkey`
+	FilesS3UsePathStyle   Key = `files.s3.usepathstyle`
+	FilesS3DisableSigning Key = `files.s3.disablesigning`
+	FilesS3TempDir        Key = `files.s3.tempdir`
 
 	MigrationTodoistEnable             Key = `migration.todoist.enable`
 	MigrationTodoistClientID           Key = `migration.todoist.clientid`
@@ -446,6 +447,7 @@ func InitDefaultConfig() {
 	FilesS3AccessKey.setDefault("")
 	FilesS3SecretKey.setDefault("")
 	FilesS3UsePathStyle.setDefault(false)
+	FilesS3DisableSigning.setDefault(false)
 	FilesS3TempDir.setDefault("")
 	// Cors
 	CorsEnable.setDefault(true)
diff --git a/pkg/files/filehandling.go b/pkg/files/filehandling.go
index e47858f6d..6cd81d568 100644
--- a/pkg/files/filehandling.go
+++ b/pkg/files/filehandling.go
@@ -33,6 +33,7 @@ import (
 	"code.vikunja.io/api/pkg/modules/keyvalue"
 
 	"github.com/aws/aws-sdk-go-v2/aws"
+	v4 "github.com/aws/aws-sdk-go-v2/aws/signer/v4"
 	awsconfig "github.com/aws/aws-sdk-go-v2/config"
 	"github.com/aws/aws-sdk-go-v2/credentials"
 	"github.com/aws/aws-sdk-go-v2/service/s3"
@@ -97,6 +98,9 @@ func initS3FileHandler() error {
 	client := s3.NewFromConfig(cfg, func(o *s3.Options) {
 		o.BaseEndpoint = aws.String(endpoint)
 		o.UsePathStyle = config.FilesS3UsePathStyle.GetBool()
+		if config.FilesS3DisableSigning.GetBool() {
+			o.APIOptions = append(o.APIOptions, v4.SwapComputePayloadSHA256ForUnsignedPayloadMiddleware)
+		}
 	})
 
 	// Initialize S3 filesystem using afero-s3