diff --git a/pyerrors/pyerrors.py b/pyerrors/pyerrors.py
index 5d54b9af..84a41f17 100644
--- a/pyerrors/pyerrors.py
+++ b/pyerrors/pyerrors.py
@@ -655,6 +655,9 @@ class CObs:
         if isinstance(self.imag, Obs):
             self.imag.gamma_method(**kwargs)
 
+    def is_zero(self):
+        return self.real == 0.0 and self.imag == 0.0
+
     def conjugate(self):
         return CObs(self.real, -self.imag)
 
@@ -678,7 +681,14 @@ class CObs:
         return -1 * (self - other)
 
     def __mul__(self, other):
-        if hasattr(other, 'real') and hasattr(other, 'imag'):
+        if all(isinstance(i, Obs) for i in [self.real, self.imag, other.real, other.imag]):
+            return CObs(derived_observable(lambda x, **kwargs: x[0] * x[1] - x[2] * x[3],
+                                           [self.real, other.real, self.imag, other.imag],
+                                           man_grad=[other.real.value, self.real.value, -other.imag.value, -self.imag.value]),
+                        derived_observable(lambda x, **kwargs: x[2] * x[1] + x[0] * x[3],
+                                           [self.real, other.real, self.imag, other.imag],
+                                           man_grad=[other.imag.value, self.imag.value, other.real.value, self.real.value]))
+        elif hasattr(other, 'real') and hasattr(other, 'imag'):
             return CObs(self.real * other.real - self.imag * other.imag,
                         self.imag * other.real + self.real * other.imag)
         else:
diff --git a/tests/test_pyerrors.py b/tests/test_pyerrors.py
index 58ec21f3..7d304464 100644
--- a/tests/test_pyerrors.py
+++ b/tests/test_pyerrors.py
@@ -204,6 +204,10 @@ def test_cobs():
     assert (my_cobs - my_cobs.conjugate()).real.is_zero()
     assert not (my_cobs - my_cobs.conjugate()).imag.is_zero()
     np.abs(my_cobs)
+
+    assert (my_cobs * my_cobs / my_cobs - my_cobs).is_zero()
+    assert (my_cobs + my_cobs - 2 * my_cobs).is_zero()
+
     fs = [[lambda x: x[0] + x[1], lambda x: x[1] + x[0]],
           [lambda x: x[0] * x[1], lambda x: x[1] * x[0]]]
     for other in [1, 1.1, (1.1-0.2j), pe.CObs(obs1), pe.CObs(obs1, obs2)]: