diff --git a/demos/Wiener_Filter.ipynb b/demos/Wiener_Filter.ipynb
index 8207b27fc83b40776a8a9d9db21d0334e5e4718b..df369506d6f0d8e9c70244d81dc3e9283467f363 100644
--- a/demos/Wiener_Filter.ipynb
+++ b/demos/Wiener_Filter.ipynb
@@ -430,7 +430,7 @@
     "mask = ift.Field.from_global_data(s_space, mask)\n",
     "\n",
     "R = ift.DiagonalOperator(mask)*HT\n",
-    "n = n.to_global_data()\n",
+    "n = n.to_global_data().copy()\n",
     "n[l:h] = 0\n",
     "n = ift.Field.from_global_data(s_space, n)\n",
     "\n",
@@ -501,7 +501,7 @@
     "m_data = HT(m).to_global_data()\n",
     "m_var_data = m_var.to_global_data()\n",
     "uncertainty = np.sqrt(m_var_data)\n",
-    "d_data = d.to_global_data()\n",
+    "d_data = d.to_global_data().copy()\n",
     "\n",
     "# Set lost data to NaN for proper plotting\n",
     "d_data[d_data == 0] = np.nan"
@@ -586,7 +586,7 @@
     "mask = ift.Field.from_global_data(s_space, mask)\n",
     "\n",
     "R = ift.DiagonalOperator(mask)*HT\n",
-    "n = n.to_global_data()\n",
+    "n = n.to_global_data().copy()\n",
     "n[l:h, l:h] = 0\n",
     "n = ift.Field.from_global_data(s_space, n)\n",
     "curv = Curvature(R=R, N=N, Sh=Sh)\n",
@@ -731,7 +731,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.6.5"
+   "version": "3.6.6"
   }
  },
  "nbformat": 4,
diff --git a/demos/getting_started_3.py b/demos/getting_started_3.py
index e66ea5edcc81711be18d8c7dd869dec91166d369..13047e0e1007433d2a8667b3d4cb8e1a89af4b02 100644
--- a/demos/getting_started_3.py
+++ b/demos/getting_started_3.py
@@ -93,12 +93,12 @@ if __name__ == '__main__':
     for sample in samples:
         sam = signal.at(sample + position).value
         powers.append(A.at(sample+position).value)
-        avrg += sam
-        va += sam**2
+        avrg = avrg + sam
+        va = va + sam**2
 
-    avrg /= len(samples)
-    va /= len(samples)
-    va -= avrg**2
+    avrg = avrg /len(samples)
+    va = va / len(samples)
+    va = va - avrg**2
     std = ift.sqrt(va)
     ift.plot(avrg, name='avrg.pdf')
     ift.plot(std, name='std.pdf')