diff --git a/backend/posix/posix_darwin.go b/backend/posix/posix_darwin.go
index c8afcb01..e67f93b8 100644
--- a/backend/posix/posix_darwin.go
+++ b/backend/posix/posix_darwin.go
@@ -32,6 +32,10 @@ type tmpfile struct {
 
 func openTmpFile(dir, bucket, obj string, size int64) (*tmpfile, error) {
 	// Create a temp file for upload while in progress (see link comments below).
+	err := os.MkdirAll(dir, 0700)
+	if err != nil {
+		return nil, fmt.Errorf("make temp dir: %w", err)
+	}
 	f, err := os.CreateTemp(dir,
 		fmt.Sprintf("%x.", sha256.Sum256([]byte(obj))))
 	if err != nil {
diff --git a/backend/posix/posix_linux.go b/backend/posix/posix_linux.go
index de83884e..9ce49d3b 100644
--- a/backend/posix/posix_linux.go
+++ b/backend/posix/posix_linux.go
@@ -47,6 +47,10 @@ func openTmpFile(dir, bucket, obj string, size int64) (*tmpfile, error) {
 	fd, err := unix.Open(dir, unix.O_RDWR|unix.O_TMPFILE|unix.O_CLOEXEC, 0666)
 	if err != nil {
 		// O_TMPFILE not supported, try fallback
+		err := os.MkdirAll(dir, 0700)
+		if err != nil {
+			return nil, fmt.Errorf("make temp dir: %w", err)
+		}
 		f, err := os.CreateTemp(dir,
 			fmt.Sprintf("%x.", sha256.Sum256([]byte(obj))))
 		if err != nil {