diff --git a/pyerrors/pyerrors.py b/pyerrors/pyerrors.py
index ba913ad8..c9b3c538 100644
--- a/pyerrors/pyerrors.py
+++ b/pyerrors/pyerrors.py
@@ -943,8 +943,8 @@ def derived_observable(func, data, **kwargs):
     n_obs = len(raveled_data)
     new_names = sorted(set([y for x in [o.names for o in raveled_data] for y in x]))
 
-    is_merged = len(list(filter(lambda o: o.is_merged is True, raveled_data))) > 1
-    reweighted = len(list(filter(lambda o: o.reweighted is True, raveled_data))) > 1
+    is_merged = len(list(filter(lambda o: o.is_merged is True, raveled_data))) > 0
+    reweighted = len(list(filter(lambda o: o.reweighted is True, raveled_data))) > 0
     new_idl_d = {}
     for name in new_names:
         idl = []
diff --git a/tests/pyerrors_test.py b/tests/pyerrors_test.py
index 1cefe09d..8b0f0704 100644
--- a/tests/pyerrors_test.py
+++ b/tests/pyerrors_test.py
@@ -276,6 +276,15 @@ def test_cobs():
         assert (other / my_cobs * my_cobs - other).is_zero()
 
 
+def test_reweighting():
+    my_obs = pe.Obs([np.random.rand(1000)], ['t'])
+    assert not my_obs.reweighted
+    r_obs = pe.reweight(my_obs, [my_obs])
+    assert r_obs[0].reweighted
+    r_obs2 = r_obs[0] * my_obs
+    assert r_obs2.reweighted
+
+
 def test_irregular_error_propagation():
     obs_list = [pe.Obs([np.random.rand(100)], ['t']),
                 pe.Obs([np.random.rand(50)], ['t'], idl=[range(1, 100, 2)]),