diff --git a/lib/light.lua b/lib/light.lua
index bfcd53e..5c7ef1d 100644
--- a/lib/light.lua
+++ b/lib/light.lua
@@ -130,7 +130,10 @@ function light:drawNormalShading(l,t,w,h,s, normalMap, shadowMap, canvas)
     self.shadowShader:send("lightAngle", math.pi - self.angle / 2.0)
     self.shadowShader:send("lightDirection", self.direction)
     self.shadowShader:send("invert_normal", self.normalInvert == true)
-    util.drawCanvasToCanvas(normalMap, canvas, {shader = self.shadowShader})
+    util.drawCanvasToCanvas(normalMap, canvas, {
+      blendmode = 'additive',
+      shader = self.shadowShader
+    })
   end
 end