diff --git a/tinygrad/tensor.py b/tinygrad/tensor.py
index 469463840d..de1329785a 100644
--- a/tinygrad/tensor.py
+++ b/tinygrad/tensor.py
@@ -514,7 +514,7 @@ class Tensor:
       return ret if bias is None else ret.add(bias.reshape(1, -1, *[1] * len(HW)))
 
     # winograd conv 3 kernel f(4x4,3x3) see: http://arxiv.org/abs/1509.09308
-    def apply_matrix(mat, t, dim=0): return t if dim == len(HW) else Tensor.stack([apply_matrix(mat, sum(mat[i][j] * t[j] for j in range(len(mat[i])) if mat[i][j]), dim=dim+1) for i in range(len(mat))])
+    def apply_matrix(mat, t, dim=0): return t if dim == len(HW) else Tensor.stack([apply_matrix(mat, sum(mm*t[j] for j,mm in enumerate(m) if mm), dim=dim+1) for m in mat])
     HWI, HWO = (6,) * len(HW), (4,) * len(HW)  # F(4x4,3x3) winograd tiles
     winograd_Bt = [[4, 0, -5, 0, 1, 0], [0, -4, -4, 1, 1, 0], [0, 4, -4, -1, 1, 0], [0, -2, -1, 2, 1, 0], [0, 2, -1, -2, 1, 0], [0, 4, 0, -5, 0, 1]]
     winograd_G = [[1/4, 0, 0], [-1/6, -1/6, -1/6], [-1/6, 1/6, -1/6], [1/24, 1/12, 1/6], [1/24, -1/12, 1/6], [0, 0, 1]]