diff --git a/brainpy/_src/math/event/csr_matvec.py b/brainpy/_src/math/event/csr_matvec.py
index dfaeba9a..dbfc2c2f 100644
--- a/brainpy/_src/math/event/csr_matvec.py
+++ b/brainpy/_src/math/event/csr_matvec.py
@@ -479,11 +479,9 @@ def _event_csr_matvec_dW(dy: ti.types.ndarray(),
                            events: ti.types.ndarray(),
                            dw: ti.types.ndarray()):
     for row_i in range(indptr.shape[0] - 1):
-      r = 0.
       for j in range(indptr[row_i], indptr[row_i + 1]):
-        if events[j] != 0.:
-          r += dy[indices[j]]
-      dw[row_i] = r
+        if events[indices[j]] != 0.:
+          dw[j] = dy[row_i]
 
 
   @ti.kernel
@@ -493,11 +491,9 @@ def _event_csr_matvec_dW_bool(dy: ti.types.ndarray(),
                                 events: ti.types.ndarray(),
                                 dw: ti.types.ndarray()):
     for row_i in range(indptr.shape[0] - 1):
-      r = 0.
       for j in range(indptr[row_i], indptr[row_i + 1]):
-        if events[j]:
-          r += dy[indices[j]]
-      dw[row_i] = r
+        if events[indices[j]]:
+          dw[j] = dy[row_i]
 
 
   def _event_csr_matvec_jvp_values_taichi(val_dot, values, indices, indptr, events, *, outs, transpose, shape):
@@ -594,4 +590,4 @@ def _define_op(cpu_kernel, gpu_kernel):
 
   # compute dW bool
   _event_csrmv_dW_bool_p = XLACustomOp(cpu_kernel=_event_csr_matvec_dW_bool,
-                                      gpu_kernel=_event_csr_matvec_dW_bool)
\ No newline at end of file
+                                       gpu_kernel=_event_csr_matvec_dW_bool)