diff --git a/cmd/stfs/cmd/serve_ftp.go b/cmd/stfs/cmd/serve_ftp.go
index de668ce..50ba1c9 100644
--- a/cmd/stfs/cmd/serve_ftp.go
+++ b/cmd/stfs/cmd/serve_ftp.go
@@ -192,7 +192,6 @@ var serveFTPCmd = &cobra.Command{
 					viper.GetString(cacheWriteFlag),
 				)
 			},
-			true, // FTP needs read permission for `STOR` command even if O_WRONLY is set
 			viper.GetBool(readOnlyFlag),
 
 			func(hdr *config.Header) {
diff --git a/cmd/stfs/cmd/serve_http.go b/cmd/stfs/cmd/serve_http.go
index ac43362..ae96b2d 100644
--- a/cmd/stfs/cmd/serve_http.go
+++ b/cmd/stfs/cmd/serve_http.go
@@ -128,10 +128,9 @@ var serveHTTPCmd = &cobra.Command{
 				Metadata: metadataPersister,
 			},
 
-			"",    // We never write
-			nil,   // We never write
-			false, // We never write
-			true,  // We never write
+			"",   // We never write
+			nil,  // We never write
+			true, // We never write
 
 			func(hdr *config.Header) {
 				jsonLogger.Trace("Header transform", hdr)
diff --git a/examples/full/main.go b/examples/full/main.go
index 6345bfa..e372356 100644
--- a/examples/full/main.go
+++ b/examples/full/main.go
@@ -171,7 +171,6 @@ func createFs(
 				writeCache,
 			)
 		},
-		false,
 		readOnly,
 
 		func(hdr *config.Header) {
diff --git a/examples/simple/main.go b/examples/simple/main.go
index 59a57e5..427dea8 100644
--- a/examples/simple/main.go
+++ b/examples/simple/main.go
@@ -99,7 +99,6 @@ func main() {
 			)
 		},
 		false,
-		false,
 
 		func(hdr *config.Header) {
 			l.Trace("Header transform", hdr)
diff --git a/pkg/fs/filesystem.go b/pkg/fs/filesystem.go
index 408bf10..67afea3 100644
--- a/pkg/fs/filesystem.go
+++ b/pkg/fs/filesystem.go
@@ -31,10 +31,9 @@ type STFS struct {
 
 	metadata config.MetadataConfig
 
-	compressionLevel           string
-	getFileBuffer              func() (cache.WriteCache, func() error, error)
-	ignoreReadWritePermissions bool
-	readOnly                   bool
+	compressionLevel string
+	getFileBuffer    func() (cache.WriteCache, func() error, error)
+	readOnly         bool
 
 	ioLock sync.Mutex
 
@@ -50,7 +49,6 @@ func NewSTFS(
 
 	compressionLevel string,
 	getFileBuffer func() (cache.WriteCache, func() error, error),
-	ignorePermissionFlags bool,
 	readOnly bool,
 
 	onHeader func(hdr *config.Header),
@@ -62,10 +60,9 @@ func NewSTFS(
 
 		metadata: metadata,
 
-		compressionLevel:           compressionLevel,
-		getFileBuffer:              getFileBuffer,
-		ignoreReadWritePermissions: ignorePermissionFlags,
-		readOnly:                   readOnly,
+		compressionLevel: compressionLevel,
+		getFileBuffer:    getFileBuffer,
+		readOnly:         readOnly,
 
 		onHeader: onHeader,
 		log:      log,
@@ -302,7 +299,7 @@ func (f *STFS) Open(name string) (afero.File, error) {
 		"name": name,
 	})
 
-	return f.OpenFile(name, os.O_RDWR, os.ModePerm)
+	return f.OpenFile(name, os.O_RDONLY, 0)
 }
 
 func (f *STFS) OpenFile(name string, flag int, perm os.FileMode) (afero.File, error) {
@@ -317,24 +314,15 @@ func (f *STFS) OpenFile(name string, flag int, perm os.FileMode) (afero.File, er
 
 	flags := &ifs.FileFlags{}
 	if f.readOnly {
-		if flag&os.O_RDONLY != 0 || flag&os.O_RDWR != 0 || f.ignoreReadWritePermissions {
+		if (flag&O_ACCMODE) == os.O_RDONLY || (flag&O_ACCMODE) == os.O_RDWR {
 			flags.Read = true
 		}
 	} else {
-		if flag&os.O_RDONLY != 0 {
+		if (flag & O_ACCMODE) == os.O_RDONLY {
 			flags.Read = true
-		}
-
-		if flag&os.O_WRONLY != 0 {
+		} else if (flag & O_ACCMODE) == os.O_WRONLY {
 			flags.Write = true
-		}
-
-		if flag&os.O_RDWR != 0 {
-			flags.Read = true
-			flags.Write = true
-		}
-
-		if f.ignoreReadWritePermissions {
+		} else if (flag & O_ACCMODE) == os.O_RDWR {
 			flags.Read = true
 			flags.Write = true
 		}
diff --git a/pkg/fs/filesystem_non_unix.go b/pkg/fs/filesystem_non_unix.go
new file mode 100644
index 0000000..b5cddc0
--- /dev/null
+++ b/pkg/fs/filesystem_non_unix.go
@@ -0,0 +1,7 @@
+//go:build windows
+
+package fs
+
+const (
+	O_ACCMODE = 0x3 // It is safe to hard-code this bit as the bits are not being set from the OS
+)
diff --git a/pkg/fs/filesystem_test.go b/pkg/fs/filesystem_test.go
index b72a5ff..1b531c1 100644
--- a/pkg/fs/filesystem_test.go
+++ b/pkg/fs/filesystem_test.go
@@ -403,7 +403,6 @@ func createSTFS(
 				writeCache,
 			)
 		},
-		false,
 		readOnly,
 
 		func(hdr *config.Header) {
diff --git a/pkg/fs/filesystem_unix.go b/pkg/fs/filesystem_unix.go
new file mode 100644
index 0000000..bb49db9
--- /dev/null
+++ b/pkg/fs/filesystem_unix.go
@@ -0,0 +1,9 @@
+//go:build !windows
+
+package fs
+
+import "syscall"
+
+const (
+	O_ACCMODE = syscall.O_ACCMODE
+)