diff --git a/wekws/model/fsmn.py b/wekws/model/fsmn.py
index 2d6a581..5a2f5fa 100644
--- a/wekws/model/fsmn.py
+++ b/wekws/model/fsmn.py
@@ -478,7 +478,7 @@ def forward(
             in_cache = [torch.zeros(0, 0, 0, 0, dtype=torch.float)
                         for _ in range(len(self.fsmn))]
         else:
-            in_cache = [in_cache[:, :, :, i:i+1] for i in range(in_cache.size(-1))]
+            in_cache = [in_cache[:, :, :, i: i+1] for i in range(in_cache.size(-1))]
         input = (input, in_cache)
         x1 = self.in_linear1(input)
         x2 = self.in_linear2(x1)