diff --git a/bin/xss-dimmer b/bin/xss-dimmer
index 265ed5d..7da0443 100755
--- a/bin/xss-dimmer
+++ b/bin/xss-dimmer
@@ -15,6 +15,7 @@ from gi.repository import Gtk, Gdk, GLib, GdkPixbuf
 import cairo
 import argparse
 import threading
+import time
 from Xlib import display, X
 from Xlib.error import BadWindow
 from Xlib.protocol.event import MapNotify
@@ -40,7 +41,7 @@ def on_realize(widget):
     window.set_override_redirect(True)
 
 
-def on_draw(widget, event, options, background, elapsed):
+def on_draw(widget, event, options, background, start):
     def _dim():
         r = cairo.Region(cairo.RectangleInt(0, 0, *widget.get_size()))
         dctx = window.begin_draw_frame(r)
@@ -52,7 +53,8 @@ def on_draw(widget, event, options, background, elapsed):
         x, y = widget.get_position()
         wwidth, wheight = widget.get_size()
         delta = options.end_opacity - options.start_opacity
-        current = elapsed[0] / options.delay
+        elapsed = time.monotonic() - start
+        current = elapsed / options.delay
         opacity = delta * current + options.start_opacity
 
         # Background
@@ -62,39 +64,41 @@ def on_draw(widget, event, options, background, elapsed):
             cctx.paint()
         else:
             scale = widget.get_scale_factor()
-            bg = background.new_subpixbuf(x, y, wwidth*scale, wheight*scale)
+            bg = background.new_subpixbuf(x, y, wwidth * scale, wheight * scale)
             cctx.save()
-            cctx.scale(1/scale, 1/scale)
+            cctx.scale(1 / scale, 1 / scale)
             Gdk.cairo_set_source_pixbuf(cctx, bg, 0, 0)
             cctx.paint_with_alpha(opacity)
             cctx.restore()
 
         # Remaining time
-        remaining = str(round(options.delay - elapsed[0]))
-        cctx.set_source_rgba(1, 1, 1, opacity)
+        if elapsed >= options.delay:
+            return
+        remaining = str(round(options.delay - elapsed))
         cctx.select_font_face(
             options.font, cairo.FONT_SLANT_NORMAL, cairo.FONT_WEIGHT_BOLD
         )
         cctx.set_font_size(wheight // 4)
         _, _, twidth, theight, _, _ = cctx.text_extents(remaining)
-        cctx.move_to(wwidth // 2 - twidth // 2, wheight // 2 + theight // 2)
+        text_position = wwidth // 2 - twidth // 2, wheight // 2 + theight // 2
+        cctx.move_to(*text_position)
+        cctx.set_source_rgba(1, 1, 1, opacity)
         cctx.show_text(remaining)
+        cctx.move_to(*text_position)
         cctx.set_source_rgba(0, 0, 0, opacity * 2)
-        cctx.move_to(wwidth // 2 - twidth // 2, wheight // 2 + theight // 2)
-        cctx.text_path(remaining)
         cctx.set_line_width(4)
+        cctx.text_path(remaining)
         cctx.stroke()
 
         # Rearm timer
         if not once:
-            elapsed[0] += options.step
-            if elapsed[0] <= options.delay:
-                GLib.timeout_add(options.step * 1000, _dim)
+            next_step = min(options.step, options.delay - elapsed)
+            on_draw.timer = GLib.timeout_add(next_step * 1000, _dim)
 
     window = widget.get_window()
-    if not elapsed:
+    dim(event)
+    if not hasattr(on_draw, "timer"):
         # First time we are called.
-        elapsed.append(0)
         dim(event)
     else:
         # Timers already running, just repaint
@@ -102,6 +106,7 @@ def on_draw(widget, event, options, background, elapsed):
 
 
 if __name__ == "__main__":
+    now = time.monotonic()
     parser = argparse.ArgumentParser()
     add = parser.add_argument
     add("--start-opacity", type=float, default=0, help="initial opacity")
@@ -134,7 +139,7 @@ if __name__ == "__main__":
         window.set_default_size(geom.width, geom.height)
         window.move(geom.x, geom.y)
 
-        window.connect("draw", on_draw, options, background, [])
+        window.connect("draw", on_draw, options, background, now)
         window.connect("delete-event", Gtk.main_quit)
         window.connect("realize", on_realize)