diff --git a/spindle/instance_lock_other.go b/spindle/instance_lock_other.go
new file mode 100644
index 000000000..3d2fa1f6f
--- /dev/null
+++ b/spindle/instance_lock_other.go
@@ -0,0 +1,5 @@
+//go:build !unix
+
+package spindle
+
+func lockInstance(string) (func(), error) { return func() {}, nil }
diff --git a/spindle/instance_lock_test.go b/spindle/instance_lock_test.go
new file mode 100644
index 000000000..6a321c6c9
--- /dev/null
+++ b/spindle/instance_lock_test.go
@@ -0,0 +1,38 @@
+//go:build unix
+
+package spindle
+
+import (
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func TestSecondSpindleOnTheSameDatabaseIsRefused(t *testing.T) {
+	dbPath := filepath.Join(t.TempDir(), "spindle.db")
+
+	release, err := lockInstance(dbPath)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err := lockInstance(dbPath); err == nil || !strings.Contains(err.Error(), "another spindle") {
+		t.Fatalf("second lock = %v, want a refusal while the first holds it", err)
+	}
+	release()
+
+	again, err := lockInstance(dbPath)
+	if err != nil {
+		t.Fatalf("the lock was not given back: %v", err)
+	}
+	again()
+}
+
+func TestNoDatabasePathMeansNoLock(t *testing.T) {
+	for range 2 {
+		release, err := lockInstance("")
+		if err != nil {
+			t.Fatal(err)
+		}
+		defer release()
+	}
+}
diff --git a/spindle/instance_lock_unix.go b/spindle/instance_lock_unix.go
new file mode 100644
index 000000000..e2b9fbabb
--- /dev/null
+++ b/spindle/instance_lock_unix.go
@@ -0,0 +1,29 @@
+//go:build unix
+
+package spindle
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"syscall"
+)
+
+// two spindles on one db would orphan workflows and double run pulls
+func lockInstance(dbPath string) (release func(), err error) {
+	if dbPath == "" {
+		return func() {}, nil
+	}
+	file, err := os.OpenFile(dbPath+".lock", os.O_CREATE|os.O_RDWR, 0o644)
+	if err != nil {
+		return nil, fmt.Errorf("opening the instance lock: %w", err)
+	}
+	if err := syscall.Flock(int(file.Fd()), syscall.LOCK_EX|syscall.LOCK_NB); err != nil {
+		_ = file.Close()
+		if errors.Is(err, syscall.EWOULDBLOCK) {
+			return nil, fmt.Errorf("another spindle is running on %s", dbPath)
+		}
+		return nil, fmt.Errorf("locking %s.lock: %w", dbPath, err)
+	}
+	return func() { _ = file.Close() }, nil
+}
diff --git a/spindle/server.go b/spindle/server.go
index 84461056d..7f1881a3a 100644
--- a/spindle/server.go
+++ b/spindle/server.go
@@ -655,6 +655,12 @@ func Run(ctx context.Context) error {
 		return fmt.Errorf("ensuring git version: %w", err)
 	}
 
+	releaseInstance, err := lockInstance(cfg.Server.DBPath)
+	if err != nil {
+		return err
+	}
+	defer releaseInstance()
+
 	d, err := db.Make(ctx, cfg.Server.DBPath)
 	if err != nil {
 		return fmt.Errorf("failed to setup db: %w", err)