diff --git a/brainpy/math/numpy_ops.py b/brainpy/math/numpy_ops.py
index 3538e84b6..fbc81be20 100644
--- a/brainpy/math/numpy_ops.py
+++ b/brainpy/math/numpy_ops.py
@@ -1521,8 +1521,11 @@ def vander(x, N=None, increasing=False):
 
 
 def fill_diagonal(a, val):
-  assert isinstance(a, JaxArray), f'Must be a JaxArray, but got {type(a)}'
-  assert a.ndim >= 2, f'Only support tensor has dimension >= 2, but got {a.shape}'
+  if not isinstance(a, JaxArray):
+    raise ValueError(f'Must be a JaxArray, but got {type(a)}')
+  if a.ndim < 2:
+    raise ValueError(f'Only support tensor has dimension >= 2, but got {a.shape}')
+  val = _remove_jaxarray(val)
   i, j = jnp.diag_indices(_min(a.shape[-2:]))
   a._value = a.value.at[..., i, j].set(val)
 
diff --git a/brainpy/math/tests/test_numpy_ops.py b/brainpy/math/tests/test_numpy_ops.py
index 0b7d41ba5..fc6e046f4 100644
--- a/brainpy/math/tests/test_numpy_ops.py
+++ b/brainpy/math/tests/test_numpy_ops.py
@@ -37,4 +37,18 @@ def test_remove_diag2(self):
     with self.assertRaises(ValueError):
       bm.remove_diag(a)
 
+  def test_fill_diagonal(self):
+    a = bm.arange(10)
+    with self.assertRaises(ValueError):
+      bm.fill_diagonal(a, 0.)
+
+    b = jnp.ones((10, 10))
+    with self.assertRaises(ValueError):
+      bm.fill_diagonal(b, 0)
+
+    bm.random.seed()
+    c = bm.random.rand(10, 10)
+    bm.fill_diagonal(c, 0)
+
+    bm.fill_diagonal(c, bm.arange(10))