diff --git a/10_Extended_Kalman_Filters.ipynb b/10_Extended_Kalman_Filters.ipynb
index c62ac5c..554fb1c 100644
--- a/10_Extended_Kalman_Filters.ipynb
+++ b/10_Extended_Kalman_Filters.ipynb
@@ -1569,7 +1569,7 @@
     "    if y[1] > np.pi:\n",
     "        y[1] -= 2*np.pi\n",
     "    if y[1] < -np.pi:\n",
-    "        y[1] = 2*np.pi\n",
+    "        y[1] += 2*np.pi\n",
     "    return y"
    ]
   },
@@ -1852,7 +1852,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.4.3"
+   "version": "3.4.1"
   }
  },
  "nbformat": 4,