diff --git a/caterva2/hdf5.py b/caterva2/hdf5.py
index fe7c4809..dfe79d45 100644
--- a/caterva2/hdf5.py
+++ b/caterva2/hdf5.py
@@ -385,6 +385,10 @@ def __init__(self, b2arr, h5file=None, dsetname=None):
     def shape(self) -> tuple[int, ...]:
         return self.b2arr.shape
 
+    @property
+    def ndim(self) -> tuple[int, ...]:
+        return self.b2arr.ndim
+
     @property
     def chunks(self):
         return self.b2arr.chunks
diff --git a/caterva2/tests/test_hdf5_proxy.py b/caterva2/tests/test_hdf5_proxy.py
index 51556744..fc6296b0 100644
--- a/caterva2/tests/test_hdf5_proxy.py
+++ b/caterva2/tests/test_hdf5_proxy.py
@@ -302,6 +302,7 @@ def test_unfold_fetch(fetch_or_slice, examples_dir, tmp_path, auth_client):
         "a ** 2.3 + b / 2.3",
         "sqrt(a) ** sin(b)",
         "where(a < 50, a + 50, b)",
+        "matmul(a, b)",
     ],
 )
 def test_expression(expression, examples_dir, tmp_path, auth_client):
@@ -331,5 +332,8 @@ def test_expression(expression, examples_dir, tmp_path, auth_client):
         # Check the data
         na = h5f[ds_a][:]
         nb = h5f[ds_b][:]
-        nresult = ne.evaluate(expression, {"a": na, "b": nb})
+        if expression != "matmul(a, b)":
+            nresult = ne.evaluate(expression, {"a": na, "b": nb})
+        else:
+            nresult = np.matmul(na, nb)
         np.testing.assert_allclose(result[:], nresult)