diff --git a/lib/mixins/vector.coffee b/lib/mixins/vector.coffee
index 9e8cf90..ee134ee 100644
--- a/lib/mixins/vector.coffee
+++ b/lib/mixins/vector.coffee
@@ -71,15 +71,21 @@ module.exports =
     @addContent "#{x} #{y} #{w} #{h} re"
     
   roundedRect: (x, y, w, h, r = 0) ->
+    r = Math.min(r, 0.5 * w, 0.5 * h)
+
+    # amount to inset control points from corners (see `ellipse`)
+    c = r * (1.0 - KAPPA)
+
     @moveTo x + r, y
     @lineTo x + w - r, y
-    @quadraticCurveTo x + w, y, x + w, y + r
+    @bezierCurveTo x + w - c, y, x + w, y + c, x + w, y + r
     @lineTo x + w, y + h - r
-    @quadraticCurveTo x + w, y + h, x + w - r, y + h
+    @bezierCurveTo x + w, y + h - c, x + w - c, y + h, x + w - r, y + h
     @lineTo x + r, y + h
-    @quadraticCurveTo x, y + h, x, y + h - r
+    @bezierCurveTo x + c, y + h, x, y + h - c, x, y + h - r
     @lineTo x, y + r
-    @quadraticCurveTo x, y, x + r, y
+    @bezierCurveTo x, y + c, x + c, y, x + r, y
+    @closePath()
     
   ellipse: (x, y, r1, r2 = r1) ->
     # based on http://stackoverflow.com/questions/2172798/how-to-draw-an-oval-in-html5-canvas/2173084#2173084