diff --git a/stim/cuda/filter.h b/stim/cuda/filter.h
index 32236f6..8e91075 100644
--- a/stim/cuda/filter.h
+++ b/stim/cuda/filter.h
@@ -19,13 +19,14 @@ texture<uchar, cudaTextureType2D, cudaReadModeElementType> texIn;
 __device__ float filterKernel ()
 {
 	float t = 0;
+	idx = j*kl+i;
 	for(int i = 0; i < kl; i++){
 		for(int j = 0; j < kl; j++){
 			x = i - floor(kl);
 			y = j - floor(kl);
-			LoG(i,j) = (-1/M_PI/sigma^4)* (1 - (x^2+y^2)/2/sigma^2)
+			LoG(idx) = (-1/M_PI/sigma^4)* (1 - (x^2+y^2)/2/sigma^2)
 					*exp(-(x^2+y^2)/2/sigma^2);	
-			t +=LoG(i,j);
+			t +=LoG(idx);
 		}
 	}
 	LoG =/ t;
--
libgit2 0.21.4