diff --git a/core/os/os.h b/core/os/os.h
index c9c228cfafd..a4f07df0e88 100644
--- a/core/os/os.h
+++ b/core/os/os.h
@@ -121,7 +121,7 @@ protected:
 	void add_logger(Logger *p_logger);
 
 	virtual void initialize_core() = 0;
-	virtual void initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver) = 0;
+	virtual Error initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver) = 0;
 
 	virtual void set_main_loop(MainLoop *p_main_loop) = 0;
 	virtual void delete_main_loop() = 0;
diff --git a/drivers/unix/os_unix.h b/drivers/unix/os_unix.h
index 7929a791cb5..d224a556474 100644
--- a/drivers/unix/os_unix.h
+++ b/drivers/unix/os_unix.h
@@ -55,7 +55,7 @@ protected:
 
 	virtual void initialize_core();
 	virtual int unix_initialize_audio(int p_audio_driver);
-	//virtual void initialize(int p_video_driver,int p_audio_driver);
+	//virtual Error initialize(int p_video_driver,int p_audio_driver);
 
 	virtual void finalize_core();
 
diff --git a/main/main.cpp b/main/main.cpp
index ac68fe12963..1cb89e87ef8 100644
--- a/main/main.cpp
+++ b/main/main.cpp
@@ -983,7 +983,10 @@ Error Main::setup2(Thread::ID p_main_tid_override) {
 		Thread::_main_thread_id = p_main_tid_override;
 	}
 
-	OS::get_singleton()->initialize(video_mode, video_driver_idx, audio_driver_idx);
+	Error err = OS::get_singleton()->initialize(video_mode, video_driver_idx, audio_driver_idx);
+	if (err != OK) {
+		return err;
+	}
 	if (init_use_custom_pos) {
 		OS::get_singleton()->set_window_position(init_custom_pos);
 	}
diff --git a/platform/android/os_android.cpp b/platform/android/os_android.cpp
index 97e81874c91..1542f4a5e46 100644
--- a/platform/android/os_android.cpp
+++ b/platform/android/os_android.cpp
@@ -120,7 +120,7 @@ void OS_Android::set_opengl_extensions(const char *p_gl_extensions) {
 	gl_extensions = p_gl_extensions;
 }
 
-void OS_Android::initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver) {
+Error OS_Android::initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver) {
 
 	use_gl2 = p_video_driver != 1;
 
@@ -146,6 +146,8 @@ void OS_Android::initialize(const VideoMode &p_desired, int p_video_driver, int
 	input->set_fallback_mapping("Default Android Gamepad");
 
 	//power_manager = memnew(power_android);
+
+	return OK;
 }
 
 void OS_Android::set_main_loop(MainLoop *p_main_loop) {
diff --git a/platform/android/os_android.h b/platform/android/os_android.h
index adfd88b59bd..c0ab2acd2e4 100644
--- a/platform/android/os_android.h
+++ b/platform/android/os_android.h
@@ -145,7 +145,7 @@ public:
 	virtual const char *get_audio_driver_name(int p_driver) const;
 
 	virtual void initialize_core();
-	virtual void initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver);
+	virtual Error initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver);
 
 	virtual void set_main_loop(MainLoop *p_main_loop);
 	virtual void delete_main_loop();
diff --git a/platform/haiku/os_haiku.cpp b/platform/haiku/os_haiku.cpp
index 65a220f8ca4..2d1d976399b 100644
--- a/platform/haiku/os_haiku.cpp
+++ b/platform/haiku/os_haiku.cpp
@@ -79,7 +79,7 @@ const char *OS_Haiku::get_video_driver_name(int p_driver) const {
 	return "GLES3";
 }
 
-void OS_Haiku::initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver) {
+Error OS_Haiku::initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver) {
 	main_loop = NULL;
 	current_video_mode = p_desired;
 
@@ -114,7 +114,7 @@ void OS_Haiku::initialize(const VideoMode &p_desired, int p_video_driver, int p_
 
 	visual_server = memnew(VisualServerRaster(rasterizer));
 
-	ERR_FAIL_COND(!visual_server);
+	ERR_FAIL_COND(!visual_server, ERR_UNAVAILABLE);
 
 	// TODO: enable multithreaded VS
 	/*
@@ -132,6 +132,8 @@ void OS_Haiku::initialize(const VideoMode &p_desired, int p_video_driver, int p_
 	AudioDriverManager::initialize(p_audio_driver);
 
 	power_manager = memnew(PowerHaiku);
+
+	return OK;
 }
 
 void OS_Haiku::finalize() {
diff --git a/platform/haiku/os_haiku.h b/platform/haiku/os_haiku.h
index 6d69c1997f7..9af15eefc07 100644
--- a/platform/haiku/os_haiku.h
+++ b/platform/haiku/os_haiku.h
@@ -66,7 +66,7 @@ protected:
 	virtual int get_video_driver_count() const;
 	virtual const char *get_video_driver_name(int p_driver) const;
 
-	virtual void initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver);
+	virtual Error initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver);
 	virtual void finalize();
 
 	virtual void set_main_loop(MainLoop *p_main_loop);
diff --git a/platform/iphone/os_iphone.cpp b/platform/iphone/os_iphone.cpp
index 507d4f22dbc..d420f95e336 100644
--- a/platform/iphone/os_iphone.cpp
+++ b/platform/iphone/os_iphone.cpp
@@ -97,7 +97,7 @@ void OSIPhone::initialize_core() {
 	set_data_dir(data_dir);
 };
 
-void OSIPhone::initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver) {
+Error OSIPhone::initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver) {
 
 	supported_orientations = 0;
 	supported_orientations |= ((GLOBAL_DEF("video_mode/allow_horizontal", true) ? 1 : 0) << LandscapeLeft);
@@ -144,6 +144,8 @@ void OSIPhone::initialize(const VideoMode &p_desired, int p_video_driver, int p_
 	//icloud->connect();
 #endif
 	Engine::get_singleton()->add_singleton(Engine::Singleton("iOS", memnew(iOS)));
+
+	return OK;
 };
 
 MainLoop *OSIPhone::get_main_loop() const {
diff --git a/platform/iphone/os_iphone.h b/platform/iphone/os_iphone.h
index 8e701a7fab8..611bc2d4cb9 100644
--- a/platform/iphone/os_iphone.h
+++ b/platform/iphone/os_iphone.h
@@ -87,7 +87,7 @@ private:
 	virtual const char *get_video_driver_name(int p_driver) const;
 
 	virtual void initialize_core();
-	virtual void initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver);
+	virtual Error initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver);
 
 	virtual void set_main_loop(MainLoop *p_main_loop);
 	virtual MainLoop *get_main_loop() const;
diff --git a/platform/javascript/os_javascript.cpp b/platform/javascript/os_javascript.cpp
index 0bdd090ba9b..665280df963 100644
--- a/platform/javascript/os_javascript.cpp
+++ b/platform/javascript/os_javascript.cpp
@@ -419,7 +419,7 @@ void send_notification(int notif) {
 }
 }
 
-void OS_JavaScript::initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver) {
+Error OS_JavaScript::initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver) {
 
 	print_line("Init OS");
 
@@ -429,7 +429,7 @@ void OS_JavaScript::initialize(const VideoMode &p_desired, int p_video_driver, i
 	attributes.antialias = false;
 	attributes.majorVersion = 2;
 	EMSCRIPTEN_WEBGL_CONTEXT_HANDLE ctx = emscripten_webgl_create_context(NULL, &attributes);
-	ERR_FAIL_COND(emscripten_webgl_make_context_current(ctx) != EMSCRIPTEN_RESULT_SUCCESS);
+	ERR_FAIL_COND(emscripten_webgl_make_context_current(ctx) != EMSCRIPTEN_RESULT_SUCCESS, ERR_UNAVAILABLE);
 
 	video_mode = p_desired;
 	// can't fulfil fullscreen request due to browser security
@@ -507,6 +507,8 @@ void OS_JavaScript::initialize(const VideoMode &p_desired, int p_video_driver, i
 #undef EM_CHECK
 
 	visual_server->init();
+
+	return OK;
 }
 
 void OS_JavaScript::set_main_loop(MainLoop *p_main_loop) {
diff --git a/platform/javascript/os_javascript.h b/platform/javascript/os_javascript.h
index 8acaac9ef38..eaf8465be94 100644
--- a/platform/javascript/os_javascript.h
+++ b/platform/javascript/os_javascript.h
@@ -82,7 +82,7 @@ public:
 	virtual const char *get_audio_driver_name(int p_driver) const;
 
 	virtual void initialize_core();
-	virtual void initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver);
+	virtual Error initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver);
 
 	virtual void set_main_loop(MainLoop *p_main_loop);
 	virtual void delete_main_loop();
diff --git a/platform/osx/os_osx.h b/platform/osx/os_osx.h
index 0411b4e72b5..2a71de12e96 100644
--- a/platform/osx/os_osx.h
+++ b/platform/osx/os_osx.h
@@ -123,7 +123,7 @@ protected:
 	virtual const char *get_video_driver_name(int p_driver) const;
 
 	virtual void initialize_core();
-	virtual void initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver);
+	virtual Error initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver);
 	virtual void finalize();
 
 	virtual void set_main_loop(MainLoop *p_main_loop);
diff --git a/platform/osx/os_osx.mm b/platform/osx/os_osx.mm
index dbc9cdf3b70..a16391c30f3 100644
--- a/platform/osx/os_osx.mm
+++ b/platform/osx/os_osx.mm
@@ -976,7 +976,7 @@ static void displays_arrangement_changed(CGDirectDisplayID display_id, CGDisplay
 	displays_arrangement_dirty = true;
 }
 
-void OS_OSX::initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver) {
+Error OS_OSX::initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver) {
 
 	/*** OSX INITIALIZATION ***/
 	/*** OSX INITIALIZATION ***/
@@ -1013,7 +1013,7 @@ void OS_OSX::initialize(const VideoMode &p_desired, int p_video_driver, int p_au
 						backing:NSBackingStoreBuffered
 						  defer:NO];
 
-	ERR_FAIL_COND(window_object == nil);
+	ERR_FAIL_COND(window_object == nil, ERR_UNAVAILABLE);
 
 	window_view = [[GodotContentView alloc] init];
 
@@ -1100,11 +1100,11 @@ void OS_OSX::initialize(const VideoMode &p_desired, int p_video_driver, int p_au
 #undef ADD_ATTR2
 
 	pixelFormat = [[NSOpenGLPixelFormat alloc] initWithAttributes:attributes];
-	ERR_FAIL_COND(pixelFormat == nil);
+	ERR_FAIL_COND(pixelFormat == nil, ERR_UNAVAILABLE);
 
 	context = [[NSOpenGLContext alloc] initWithFormat:pixelFormat shareContext:nil];
 
-	ERR_FAIL_COND(context == nil);
+	ERR_FAIL_COND(context == nil, ERR_UNAVAILABLE);
 
 	[context setView:window_view];
 
@@ -1148,6 +1148,8 @@ void OS_OSX::initialize(const VideoMode &p_desired, int p_video_driver, int p_au
 	_ensure_user_data_dir();
 
 	restore_rect = Rect2(get_window_position(), get_window_size());
+
+	return OK;
 }
 
 void OS_OSX::finalize() {
diff --git a/platform/server/os_server.cpp b/platform/server/os_server.cpp
index 13264ed46e0..e8d076322c0 100644
--- a/platform/server/os_server.cpp
+++ b/platform/server/os_server.cpp
@@ -47,7 +47,7 @@ const char *OS_Server::get_video_driver_name(int p_driver) const {
 	return "Dummy";
 }
 
-void OS_Server::initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver) {
+Error OS_Server::initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver) {
 
 	args = OS::get_singleton()->get_cmdline_args();
 	current_videomode = p_desired;
@@ -67,13 +67,15 @@ void OS_Server::initialize(const VideoMode &p_desired, int p_video_driver, int p
 	spatial_sound_2d_server = memnew(SpatialSound2DServerSW);
 	spatial_sound_2d_server->init();
 
-	ERR_FAIL_COND(!visual_server);
+	ERR_FAIL_COND(!visual_server, ERR_UNAVAILABLE);
 
 	visual_server->init();
 
 	input = memnew(InputDefault);
 
 	_ensure_user_data_dir();
+
+	return OK;
 }
 void OS_Server::finalize() {
 
diff --git a/platform/server/os_server.h b/platform/server/os_server.h
index 7b7d4a38a84..67393754680 100644
--- a/platform/server/os_server.h
+++ b/platform/server/os_server.h
@@ -66,7 +66,7 @@ protected:
 	virtual int get_video_driver_count() const;
 	virtual const char *get_video_driver_name(int p_driver) const;
 
-	virtual void initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver);
+	virtual Error initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver);
 	virtual void finalize();
 
 	virtual void set_main_loop(MainLoop *p_main_loop);
diff --git a/platform/uwp/os_uwp.cpp b/platform/uwp/os_uwp.cpp
index 603a918cca3..96f9c895bcd 100644
--- a/platform/uwp/os_uwp.cpp
+++ b/platform/uwp/os_uwp.cpp
@@ -194,7 +194,7 @@ void OSUWP::screen_size_changed() {
 	gl_context->reset();
 };
 
-void OSUWP::initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver) {
+Error OSUWP::initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver) {
 
 	main_loop = NULL;
 	outside = true;
@@ -297,6 +297,8 @@ void OSUWP::initialize(const VideoMode &p_desired, int p_video_driver, int p_aud
 		display_request->RequestActive();
 
 	set_keep_screen_on(GLOBAL_DEF("display/window/keep_screen_on", true));
+
+	return OK;
 }
 
 void OSUWP::set_clipboard(const String &p_text) {
diff --git a/platform/uwp/os_uwp.h b/platform/uwp/os_uwp.h
index 976eda1fe12..ad12b6286f1 100644
--- a/platform/uwp/os_uwp.h
+++ b/platform/uwp/os_uwp.h
@@ -158,7 +158,7 @@ protected:
 	virtual const char *get_audio_driver_name(int p_driver) const;
 
 	virtual void initialize_core();
-	virtual void initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver);
+	virtual Error initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver);
 
 	virtual void set_main_loop(MainLoop *p_main_loop);
 	virtual void delete_main_loop();
diff --git a/platform/windows/os_windows.cpp b/platform/windows/os_windows.cpp
index e3af82b629d..a48ae8cc8c7 100644
--- a/platform/windows/os_windows.cpp
+++ b/platform/windows/os_windows.cpp
@@ -929,7 +929,7 @@ typedef enum _SHC_PROCESS_DPI_AWARENESS {
 	SHC_PROCESS_PER_MONITOR_DPI_AWARE = 2
 } SHC_PROCESS_DPI_AWARENESS;
 
-void OS_Windows::initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver) {
+Error OS_Windows::initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver) {
 
 	main_loop = NULL;
 	outside = true;
@@ -975,7 +975,7 @@ void OS_Windows::initialize(const VideoMode &p_desired, int p_video_driver, int
 
 	if (!RegisterClassExW(&wc)) {
 		MessageBox(NULL, "Failed To Register The Window Class.", "ERROR", MB_OK | MB_ICONEXCLAMATION);
-		return; // Return
+		return ERR_UNAVAILABLE;
 	}
 
 	pre_fs_valid = true;
@@ -1045,7 +1045,7 @@ void OS_Windows::initialize(const VideoMode &p_desired, int p_video_driver, int
 		RECT rect;
 		if (!GetClientRect(hWnd, &rect)) {
 			MessageBoxW(NULL, L"Window Creation Error.", L"ERROR", MB_OK | MB_ICONEXCLAMATION);
-			return; // Return FALSE
+			return ERR_UNAVAILABLE;
 		};
 		video_mode.width = rect.right;
 		video_mode.height = rect.bottom;
@@ -1063,7 +1063,7 @@ void OS_Windows::initialize(const VideoMode &p_desired, int p_video_driver, int
 				NULL, NULL, hInstance, NULL);
 		if (!hWnd) {
 			MessageBoxW(NULL, L"Window Creation Error.", L"ERROR", MB_OK | MB_ICONEXCLAMATION);
-			return; // Return FALSE
+			return ERR_UNAVAILABLE;
 		}
 	};
 
@@ -1127,6 +1127,8 @@ void OS_Windows::initialize(const VideoMode &p_desired, int p_video_driver, int
 		SetForegroundWindow(hWnd); // Slightly Higher Priority
 		SetFocus(hWnd); // Sets Keyboard Focus To
 	}
+
+	return OK;
 }
 
 void OS_Windows::set_clipboard(const String &p_text) {
diff --git a/platform/windows/os_windows.h b/platform/windows/os_windows.h
index 9d254ccf27b..1863642f398 100644
--- a/platform/windows/os_windows.h
+++ b/platform/windows/os_windows.h
@@ -148,7 +148,7 @@ protected:
 	virtual const char *get_audio_driver_name(int p_driver) const;
 
 	virtual void initialize_core();
-	virtual void initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver);
+	virtual Error initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver);
 
 	virtual void set_main_loop(MainLoop *p_main_loop);
 	virtual void delete_main_loop();
diff --git a/platform/x11/os_x11.cpp b/platform/x11/os_x11.cpp
index e9920b18a4d..5ca3ad45b81 100644
--- a/platform/x11/os_x11.cpp
+++ b/platform/x11/os_x11.cpp
@@ -100,7 +100,7 @@ void OS_X11::initialize_core() {
 	OS_Unix::initialize_core();
 }
 
-void OS_X11::initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver) {
+Error OS_X11::initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver) {
 
 	long im_event_mask = 0;
 	last_button_state = 0;
@@ -123,21 +123,24 @@ void OS_X11::initialize(const VideoMode &p_desired, int p_video_driver, int p_au
 	/** XLIB INITIALIZATION **/
 	x11_display = XOpenDisplay(NULL);
 
+	if (!x11_display) {
+		ERR_PRINT("X11 Display is not available");
+		return ERR_UNAVAILABLE;
+	}
+
 	char *modifiers = NULL;
 	Bool xkb_dar = False;
-	if (x11_display) {
-		XAutoRepeatOn(x11_display);
-		xkb_dar = XkbSetDetectableAutoRepeat(x11_display, True, NULL);
+	XAutoRepeatOn(x11_display);
+	xkb_dar = XkbSetDetectableAutoRepeat(x11_display, True, NULL);
 
-		// Try to support IME if detectable auto-repeat is supported
-		if (xkb_dar == True) {
+	// Try to support IME if detectable auto-repeat is supported
+	if (xkb_dar == True) {
 
 #ifdef X_HAVE_UTF8_STRING
-			// Xutf8LookupString will be used later instead of XmbLookupString before
-			// the multibyte sequences can be converted to unicode string.
-			modifiers = XSetLocaleModifiers("");
+		// Xutf8LookupString will be used later instead of XmbLookupString before
+		// the multibyte sequences can be converted to unicode string.
+		modifiers = XSetLocaleModifiers("");
 #endif
-		}
 	}
 
 	if (modifiers == NULL) {
@@ -331,8 +334,8 @@ void OS_X11::initialize(const VideoMode &p_desired, int p_video_driver, int p_au
 
 	AudioDriverManager::initialize(p_audio_driver);
 
-	ERR_FAIL_COND(!visual_server);
-	ERR_FAIL_COND(x11_window == 0);
+	ERR_FAIL_COND_V(!visual_server, ERR_UNAVAILABLE);
+	ERR_FAIL_COND_V(x11_window == 0, ERR_UNAVAILABLE);
 
 	XSetWindowAttributes new_attr;
 
diff --git a/platform/x11/os_x11.h b/platform/x11/os_x11.h
index 04243a9b36c..2bf2f3cf265 100644
--- a/platform/x11/os_x11.h
+++ b/platform/x11/os_x11.h
@@ -193,7 +193,7 @@ protected:
 	virtual const char *get_audio_driver_name(int p_driver) const;
 
 	virtual void initialize_core();
-	virtual void initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver);
+	virtual Error initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver);
 	virtual void finalize();
 
 	virtual void set_main_loop(MainLoop *p_main_loop);