diff --git a/src/register_types.cpp b/src/register_types.cpp
index 985fa9a..08e3e47 100644
--- a/src/register_types.cpp
+++ b/src/register_types.cpp
@@ -30,7 +30,7 @@ void uninitialize_scene_types() {
   script_loader.unref();
 }
 
-static SchemeReplServer *repl_server;
+static SchemeReplServer *repl_server = nullptr;
 
 void initialize_server_types() {
   GDREGISTER_CLASS(SchemeReplServer);
diff --git a/src/scheme.cpp b/src/scheme.cpp
index ed1638a..5c3f8f3 100644
--- a/src/scheme.cpp
+++ b/src/scheme.cpp
@@ -25,12 +25,15 @@ void Scheme::_process(double delta) {
 }
 void Scheme::_enter_tree() {
   // TODO: move initialization here
-  SchemeReplServer::get_singleton()->publish_node(this);
+  auto server = SchemeReplServer::get_singleton();
+  if (server) server->publish_node(this);
+
   Node::_enter_tree();
 }
 
 void Scheme::_exit_tree() {
-  SchemeReplServer::get_singleton()->unpublish_node(this);
+  auto server = SchemeReplServer::get_singleton();
+  if (server) server->unpublish_node(this);
 
   if (_process_symbol) {
     auto _ = scheme.call_optional("_exit_tree");
diff --git a/src/scheme_repl_server.cpp b/src/scheme_repl_server.cpp
index 820ae7e..e4e5e64 100644
--- a/src/scheme_repl_server.cpp
+++ b/src/scheme_repl_server.cpp
@@ -90,7 +90,7 @@ void SchemeReplServer::stop() {
   thread.unref();
 }
 
-SchemeReplServer *SchemeReplServer::singleton = NULL;
+SchemeReplServer *SchemeReplServer::singleton = nullptr;
 
 SchemeReplServer *SchemeReplServer::get_singleton() {
   return singleton;
@@ -100,6 +100,10 @@ SchemeReplServer::SchemeReplServer() {
   singleton = this;
 }
 
+SchemeReplServer::~SchemeReplServer() {
+  singleton = nullptr;
+}
+
 void SchemeReplServer::_bind_methods() {
   ClassDB::bind_method(D_METHOD("server_loop"), &SchemeReplServer::server_loop);
   ClassDB::bind_method(D_METHOD("reply"), &SchemeReplServer::reply);
diff --git a/src/scheme_repl_server.hpp b/src/scheme_repl_server.hpp
index 141c2ee..7a29263 100644
--- a/src/scheme_repl_server.hpp
+++ b/src/scheme_repl_server.hpp
@@ -26,6 +26,7 @@ class SchemeReplServer : public Object {
 
 public: // extension initialization API
   SchemeReplServer();
+  ~SchemeReplServer();
   Error start();
   void stop();