diff --git a/src/CanvasRenderingContext2d.cc b/src/CanvasRenderingContext2d.cc
index 527db5a..f755945 100644
--- a/src/CanvasRenderingContext2d.cc
+++ b/src/CanvasRenderingContext2d.cc
@@ -325,7 +325,7 @@ void
 Context2d::blur(cairo_surface_t *surface, int radius) {
   // Steve Hanov, 2009
   // Released into the public domain.
-  
+  --radius;
   // get width, height
   int width = cairo_image_surface_get_width( surface );
   int height = cairo_image_surface_get_height( surface );