diff --git a/brainpy/connect/tests/test_regular_conn.py b/brainpy/connect/tests/test_regular_conn.py
index f2f464670..f6d9e79a7 100644
--- a/brainpy/connect/tests/test_regular_conn.py
+++ b/brainpy/connect/tests/test_regular_conn.py
@@ -14,7 +14,7 @@ def test_one2one():
     num = bp.tools.size2num(size)
 
     actual_mat = bp.math.zeros((num, num), dtype=bp.math.bool_)
-    actual_mat = bp.math.fill_diagonal(actual_mat, True)
+    bp.math.fill_diagonal(actual_mat, True)
 
     assert bp.math.array_equal(actual_mat, conn_mat)
     assert bp.math.array_equal(pre_ids, bp.math.arange(num))
@@ -42,7 +42,7 @@ def test_all2all():
       print(mat)
       actual_mat = bp.math.ones((num, num), dtype=bp.math.bool_)
       if not has_self:
-        actual_mat = bp.math.fill_diagonal(actual_mat, False)
+        bp.math.fill_diagonal(actual_mat, False)
 
       assert bp.math.array_equal(actual_mat, mat)
 
diff --git a/brainpy/math/delay_vars.py b/brainpy/math/delay_vars.py
index 4b2ffb3b4..a18a7c5bd 100644
--- a/brainpy/math/delay_vars.py
+++ b/brainpy/math/delay_vars.py
@@ -168,6 +168,7 @@ def __init__(
 
   def _check_time(self, times, transforms):
     prev_time, current_time = times
+    current_time = current_time[0]
     if prev_time > current_time + 1e-6:
       raise ValueError(f'\n'
                        f'!!! Error in {self.__class__.__name__}: \n'
@@ -194,7 +195,7 @@ def __call__(self, time, indices=None):
       return self._after_t0(time)
 
   def _after_t0(self, prev_time):
-    diff = self.delay_len - (self.current_time - prev_time)
+    diff = self.delay_len - (self.current_time[0] - prev_time)
     if isinstance(diff, ndarray):
       diff = diff.value
     if self.interp_method == _INTERP_LINEAR: