diff --git a/pyerrors/obs.py b/pyerrors/obs.py
index a49320a5..e00a3241 100644
--- a/pyerrors/obs.py
+++ b/pyerrors/obs.py
@@ -278,7 +278,7 @@ class Obs:
 
             def _compute_drho(i):
                 tmp = (self.e_rho[e_name][i + 1:w_max]
-                       + np.concatenate([self.e_rho[e_name][i - 1:None if i - w_max // 2 <= 0 else 2 * (i - w_max // 2):-1],
+                       + np.concatenate([self.e_rho[e_name][i - 1:None if i - w_max // 2 <= 0 else (2 * i - (2 * w_max) // 2):-1],
                                          self.e_rho[e_name][1:max(1, w_max - 2 * i)]])
                        - 2 * self.e_rho[e_name][i] * self.e_rho[e_name][1:w_max - i])
                 self.e_drho[e_name][i] = np.sqrt(np.sum(tmp ** 2) / e_N)
diff --git a/tests/obs_test.py b/tests/obs_test.py
index 084edd64..d5d8d5e1 100644
--- a/tests/obs_test.py
+++ b/tests/obs_test.py
@@ -762,11 +762,22 @@ def test_gamma_method_irregular():
     N = 15
     for i in range(10):
         arr = np.random.normal(1, .2, size=N)
-        for rho in .1 * np.arange(20):
+        for rho in .05 * np.arange(20):
             carr = gen_autocorrelated_array(arr, rho)
             a = pe.Obs([carr], ['a'])
             a.gm()
 
+    arr = np.random.normal(1, .2, size=999)
+    carr = gen_autocorrelated_array(arr, .8)
+    o = pe.Obs([carr], ['test'])
+    o.gamma_method()
+    no = np.NaN * o
+    no.gamma_method()
+    o.idl['test'] = range(1, 1998, 2)
+    o.gamma_method()
+    no = np.NaN * o
+    no.gamma_method()
+
 
 def test_irregular_gapped_dtauint():
     my_idl = list(range(0, 5010, 10))
@@ -1096,7 +1107,7 @@ def test_reduce_deltas():
     for idx_new in idl:
         new = pe.obs._reduce_deltas(deltas, idx_old, idx_new)
         print(new)
-        assert(np.alltrue([float(i) for i in idx_new] == new))
+        assert(np.all([float(i) for i in idx_new] == new))
 
 
 def test_cobs_array():