diff --git a/docs/examples/sigmoid.ipynb b/docs/examples/sigmoid.ipynb
index a7634d5..09cf2cf 100644
--- a/docs/examples/sigmoid.ipynb
+++ b/docs/examples/sigmoid.ipynb
@@ -47,7 +47,7 @@
     "    fpp = fp*(1-2*fo)\n",
     "    fppp = fpp*(1-4*fo)\n",
     "    d = x-xo\n",
-    "    y = fo + fp*d + 0.5*fpp*d**2 + (1.0/6.0)*fppp*d**3\n",
+    "    y = fo + fp*d + 0.5*fpp*np.power(d,2) + (1.0/6.0)*fppp*np.power(d,3)\n",
     "    return y\n",
     "\n",
     "# Want to evaluate sigmoid here\n",