diff --git a/backend/wayland/output.c b/backend/wayland/output.c
index c4301617..f6182dcd 100644
--- a/backend/wayland/output.c
+++ b/backend/wayland/output.c
@@ -28,6 +28,15 @@ static struct wl_callback_listener frame_listener = {
 	.done = surface_frame_callback
 };
 
+static bool wlr_wl_output_set_custom_mode(struct wlr_output *_output,
+		int32_t width, int32_t height, int32_t refresh) {
+	struct wlr_wl_backend_output *output = (struct wlr_wl_backend_output *)_output;
+	wl_egl_window_resize(output->egl_window, width, height, 0, 0);
+	wlr_output_update_size(&output->wlr_output, width, height);
+	wl_signal_emit(&output->wlr_output.events.resolution, output);
+	return true;
+}
+
 static void wlr_wl_output_make_current(struct wlr_output *_output) {
 	struct wlr_wl_backend_output *output = (struct wlr_wl_backend_output *)_output;
 	if (!eglMakeCurrent(output->backend->egl.display,
@@ -185,6 +194,7 @@ bool wlr_wl_output_move_cursor(struct wlr_output *_output, int x, int y) {
 }
 
 static struct wlr_output_impl output_impl = {
+	.set_custom_mode = wlr_wl_output_set_custom_mode,
 	.transform = wlr_wl_output_transform,
 	.destroy = wlr_wl_output_destroy,
 	.make_current = wlr_wl_output_make_current,
diff --git a/backend/x11/backend.c b/backend/x11/backend.c
index b798daf6..5fb54ffd 100644
--- a/backend/x11/backend.c
+++ b/backend/x11/backend.c
@@ -267,8 +267,8 @@ static bool wlr_x11_backend_start(struct wlr_backend *backend) {
 	snprintf(output->wlr_output.name, sizeof(output->wlr_output.name), "X11-1");
 
 	output->win = xcb_generate_id(x11->xcb_conn);
-	xcb_create_window(x11->xcb_conn, XCB_COPY_FROM_PARENT, output->win, x11->screen->root,
-		0, 0, 1024, 768, 1, XCB_WINDOW_CLASS_INPUT_OUTPUT,
+	xcb_create_window(x11->xcb_conn, XCB_COPY_FROM_PARENT, output->win,
+		x11->screen->root, 0, 0, 1024, 768, 1, XCB_WINDOW_CLASS_INPUT_OUTPUT,
 		x11->screen->root_visual, mask, values);
 
 	output->surf = wlr_egl_create_surface(&x11->egl, &output->win);
@@ -329,6 +329,17 @@ static struct wlr_backend_impl backend_impl = {
 	.get_egl = wlr_x11_backend_get_egl,
 };
 
+static bool output_set_custom_mode(struct wlr_output *wlr_output, int32_t width,
+		int32_t height, int32_t refresh) {
+	struct wlr_x11_output *output = (struct wlr_x11_output *)wlr_output;
+	struct wlr_x11_backend *x11 = output->x11;
+
+	const uint32_t values[] = { width, height };
+	xcb_configure_window(x11->xcb_conn, output->win,
+		XCB_CONFIG_WINDOW_WIDTH | XCB_CONFIG_WINDOW_HEIGHT, values);
+	return true;
+}
+
 static void output_transform(struct wlr_output *wlr_output, enum wl_output_transform transform) {
 	struct wlr_x11_output *output = (struct wlr_x11_output *)wlr_output;
 	output->wlr_output.transform = transform;
@@ -362,6 +373,7 @@ static void output_swap_buffers(struct wlr_output *wlr_output) {
 }
 
 static struct wlr_output_impl output_impl = {
+	.set_custom_mode = output_set_custom_mode,
 	.transform = output_transform,
 	.destroy = output_destroy,
 	.make_current = output_make_current,
diff --git a/include/wlr/interfaces/wlr_output.h b/include/wlr/interfaces/wlr_output.h
index b4f39d35..dc2a867b 100644
--- a/include/wlr/interfaces/wlr_output.h
+++ b/include/wlr/interfaces/wlr_output.h
@@ -9,6 +9,8 @@
 struct wlr_output_impl {
 	void (*enable)(struct wlr_output *output, bool enable);
 	bool (*set_mode)(struct wlr_output *output, struct wlr_output_mode *mode);
+	bool (*set_custom_mode)(struct wlr_output *output, int32_t width,
+		int32_t height, int32_t refresh);
 	void (*transform)(struct wlr_output *output,
 		enum wl_output_transform transform);
 	bool (*set_cursor)(struct wlr_output *output, const uint8_t *buf,
diff --git a/include/wlr/types/wlr_output.h b/include/wlr/types/wlr_output.h
index 895536e1..7f681ab7 100644
--- a/include/wlr/types/wlr_output.h
+++ b/include/wlr/types/wlr_output.h
@@ -83,6 +83,8 @@ struct wlr_surface;
 void wlr_output_enable(struct wlr_output *output, bool enable);
 bool wlr_output_set_mode(struct wlr_output *output,
 	struct wlr_output_mode *mode);
+bool wlr_output_set_custom_mode(struct wlr_output *output, int32_t width,
+	int32_t height, int32_t refresh);
 void wlr_output_transform(struct wlr_output *output,
 	enum wl_output_transform transform);
 void wlr_output_set_position(struct wlr_output *output, int32_t lx, int32_t ly);
diff --git a/rootston/output.c b/rootston/output.c
index cf2ffdc3..b2d6554d 100644
--- a/rootston/output.c
+++ b/rootston/output.c
@@ -263,8 +263,15 @@ static void output_frame_notify(struct wl_listener *listener, void *data) {
 
 static void set_mode(struct wlr_output *output,
 		struct roots_output_config *oc) {
-	struct wlr_output_mode *mode, *best = NULL;
 	int mhz = (int)(oc->mode.refresh_rate * 1000);
+
+	if (wl_list_empty(&output->modes)) {
+		// Output has no mode, try setting a custom one
+		wlr_output_set_custom_mode(output, oc->mode.width, oc->mode.height, mhz);
+		return;
+	}
+
+	struct wlr_output_mode *mode, *best = NULL;
 	wl_list_for_each(mode, &output->modes, link) {
 		if (mode->width == oc->mode.width && mode->height == oc->mode.height) {
 			if (mode->refresh == mhz) {
diff --git a/types/wlr_output.c b/types/wlr_output.c
index f4ae7aaa..adade238 100644
--- a/types/wlr_output.c
+++ b/types/wlr_output.c
@@ -164,6 +164,23 @@ bool wlr_output_set_mode(struct wlr_output *output,
 	return result;
 }
 
+bool wlr_output_set_custom_mode(struct wlr_output *output, int32_t width,
+		int32_t height, int32_t refresh) {
+	if (!output->impl || !output->impl->set_custom_mode) {
+		return false;
+	}
+	bool result = output->impl->set_custom_mode(output, width, height, refresh);
+	if (result) {
+		wlr_output_update_matrix(output);
+
+		struct wl_resource *resource;
+		wl_resource_for_each(resource, &output->wl_resources) {
+			wlr_output_send_current_mode_to_resource(resource);
+		}
+	}
+	return result;
+}
+
 void wlr_output_update_size(struct wlr_output *output, int32_t width,
 		int32_t height) {
 	if (output->width == width && output->height == height) {