diff --git a/brainpy/_src/math/delayvars.py b/brainpy/_src/math/delayvars.py
index 390e04dd7..676e4286b 100644
--- a/brainpy/_src/math/delayvars.py
+++ b/brainpy/_src/math/delayvars.py
@@ -473,7 +473,7 @@ def update(self, value: Union[numbers.Number, Array, jax.Array] = None):
 
     elif self.update_method == CONCAT_UPDATE:
       if self.num_delay_step >= 2:
-        self.data.value = concatenate([expand_dims(value, 0), self.data[1:]], axis=0)
+        self.data.value = concatenate([expand_dims(value, 0), self.data[:-1]], axis=0)
       else:
         self.data[:] = value