diff --git a/pyerrors/obs.py b/pyerrors/obs.py
index e925c51b..35c97454 100644
--- a/pyerrors/obs.py
+++ b/pyerrors/obs.py
@@ -459,7 +459,7 @@ class Obs:
         atol : float
             Absolute tolerance (for details see numpy documentation).
         """
-        return (np.isclose(0.0, self.value, rtol, atol) and all(np.allclose(0.0, delta, rtol, atol) for delta in self.deltas.values()) and all(np.allclose(0.0, delta.grad, rtol, atol) for delta in self.covobs.values()))
+        return np.isclose(0.0, self.value, rtol, atol) and all(np.allclose(0.0, delta, rtol, atol) for delta in self.deltas.values()) and all(np.allclose(0.0, delta.errsq(), rtol, atol) for delta in self.covobs.values())
 
     def plot_tauint(self, save=None):
         """Plot integrated autocorrelation time for each ensemble.
diff --git a/tests/obs_test.py b/tests/obs_test.py
index 8af54d56..d93fbe5f 100644
--- a/tests/obs_test.py
+++ b/tests/obs_test.py
@@ -581,3 +581,9 @@ def test_covobs():
 
     do = cl[0] * cl[1]
     assert(np.array_equal(do.covobs['rAP'].grad, np.transpose([pi[1], pi[0]]).reshape(2, 1)))
+
+
+def test_covobs_overloading():
+    covobs = pe.cov_Obs([0.5, 0.5], np.array([[0.02, 0.02], [0.02, 0.02]]), 'Zfactor')
+    assert (covobs[0] / covobs[1]) == 1
+    assert (covobs[0] - covobs[1]) == 0