diff --git a/main/main.cpp b/main/main.cpp
index 551b5ccf5d9..c6bac052d2d 100644
--- a/main/main.cpp
+++ b/main/main.cpp
@@ -1118,9 +1118,13 @@ Error Main::setup(const char *execpath, int argc, char *argv[], bool p_second_ph
 	}
 
 	if (rtm >= 0 && rtm < 3) {
+#ifdef NO_THREADS
+		rtm = OS::RENDER_THREAD_UNSAFE; // No threads available on this platform.
+#else
 		if (editor) {
 			rtm = OS::RENDER_THREAD_SAFE;
 		}
+#endif
 		OS::get_singleton()->_render_thread_mode = OS::RenderThreadMode(rtm);
 	}
 
diff --git a/servers/physics_2d/physics_2d_server_sw.cpp b/servers/physics_2d/physics_2d_server_sw.cpp
index be8e1a7a33d..2a7d887fd44 100644
--- a/servers/physics_2d/physics_2d_server_sw.cpp
+++ b/servers/physics_2d/physics_2d_server_sw.cpp
@@ -1455,7 +1455,11 @@ Physics2DServerSW::Physics2DServerSW() {
 	island_count = 0;
 	active_objects = 0;
 	collision_pairs = 0;
+#ifdef NO_THREADS
+	using_threads = false;
+#else
 	using_threads = int(ProjectSettings::get_singleton()->get("physics/2d/thread_model")) == 2;
+#endif
 	flushing_queries = false;
 };
 
diff --git a/servers/physics_2d/physics_2d_server_wrap_mt.h b/servers/physics_2d/physics_2d_server_wrap_mt.h
index eec0a3933f6..38ca6099bc4 100644
--- a/servers/physics_2d/physics_2d_server_wrap_mt.h
+++ b/servers/physics_2d/physics_2d_server_wrap_mt.h
@@ -326,6 +326,9 @@ public:
 	template <class T>
 	static Physics2DServer *init_server() {
 
+#ifdef NO_THREADS
+		return memnew(T); // Always single unsafe when no threads are available.
+#else
 		int tm = GLOBAL_DEF("physics/2d/thread_model", 1);
 		if (tm == 0) // single unsafe
 			return memnew(T);
@@ -333,6 +336,7 @@ public:
 			return memnew(Physics2DServerWrapMT(memnew(T), false));
 		else // multi threaded
 			return memnew(Physics2DServerWrapMT(memnew(T), true));
+#endif
 	}
 
 #undef ServerNameWrapMT