diff --git a/Delta-Intro.ipynb b/Delta-Intro.ipynb
index 7945fc3..a86484f 100644
--- a/Delta-Intro.ipynb
+++ b/Delta-Intro.ipynb
@@ -3,8 +3,6 @@
   {
    "cell_type": "markdown",
    "metadata": {
-    "deletable": true,
-    "editable": true,
     "slideshow": {
      "slide_type": "slide"
     }
@@ -17,9 +15,6 @@
    "cell_type": "code",
    "execution_count": 1,
    "metadata": {
-    "collapsed": false,
-    "deletable": true,
-    "editable": true,
     "slideshow": {
      "slide_type": "slide"
     }
@@ -56,8 +51,6 @@
   {
    "cell_type": "markdown",
    "metadata": {
-    "deletable": true,
-    "editable": true,
     "slideshow": {
      "slide_type": "slide"
     }
@@ -70,9 +63,6 @@
    "cell_type": "code",
    "execution_count": 2,
    "metadata": {
-    "collapsed": false,
-    "deletable": true,
-    "editable": true,
     "slideshow": {
      "slide_type": "-"
     }
@@ -86,8 +76,6 @@
   {
    "cell_type": "markdown",
    "metadata": {
-    "deletable": true,
-    "editable": true,
     "slideshow": {
      "slide_type": "slide"
     }
@@ -100,9 +88,6 @@
    "cell_type": "code",
    "execution_count": 3,
    "metadata": {
-    "collapsed": false,
-    "deletable": true,
-    "editable": true,
     "slideshow": {
      "slide_type": "-"
     }
@@ -355,9 +340,6 @@
    "cell_type": "code",
    "execution_count": 4,
    "metadata": {
-    "collapsed": false,
-    "deletable": true,
-    "editable": true,
     "slideshow": {
      "slide_type": "subslide"
     }
@@ -382,9 +364,6 @@
    "cell_type": "code",
    "execution_count": 5,
    "metadata": {
-    "collapsed": false,
-    "deletable": true,
-    "editable": true,
     "slideshow": {
      "slide_type": "-"
     }
@@ -408,8 +387,6 @@
   {
    "cell_type": "markdown",
    "metadata": {
-    "deletable": true,
-    "editable": true,
     "slideshow": {
      "slide_type": "slide"
     }
@@ -421,11 +398,7 @@
   {
    "cell_type": "code",
    "execution_count": 6,
-   "metadata": {
-    "collapsed": false,
-    "deletable": true,
-    "editable": true
-   },
+   "metadata": {},
    "outputs": [
     {
      "data": {
@@ -446,8 +419,6 @@
   {
    "cell_type": "markdown",
    "metadata": {
-    "deletable": true,
-    "editable": true,
     "slideshow": {
      "slide_type": "subslide"
     }
@@ -460,9 +431,6 @@
    "cell_type": "code",
    "execution_count": 7,
    "metadata": {
-    "collapsed": false,
-    "deletable": true,
-    "editable": true,
     "slideshow": {
      "slide_type": "-"
     }
@@ -499,8 +467,6 @@
   {
    "cell_type": "markdown",
    "metadata": {
-    "deletable": true,
-    "editable": true,
     "slideshow": {
      "slide_type": "slide"
     }
@@ -515,9 +481,6 @@
    "cell_type": "code",
    "execution_count": 8,
    "metadata": {
-    "collapsed": false,
-    "deletable": true,
-    "editable": true,
     "slideshow": {
      "slide_type": "-"
     }
@@ -568,8 +531,6 @@
   {
    "cell_type": "markdown",
    "metadata": {
-    "deletable": true,
-    "editable": true,
     "slideshow": {
      "slide_type": "subslide"
     }
@@ -582,9 +543,6 @@
    "cell_type": "code",
    "execution_count": 9,
    "metadata": {
-    "collapsed": false,
-    "deletable": true,
-    "editable": true,
     "slideshow": {
      "slide_type": "fragment"
     }
@@ -610,8 +568,6 @@
   {
    "cell_type": "markdown",
    "metadata": {
-    "deletable": true,
-    "editable": true,
     "slideshow": {
      "slide_type": "fragment"
     }
@@ -624,9 +580,6 @@
    "cell_type": "code",
    "execution_count": 10,
    "metadata": {
-    "collapsed": false,
-    "deletable": true,
-    "editable": true,
     "slideshow": {
      "slide_type": "fragment"
     }
@@ -652,9 +605,6 @@
    "cell_type": "code",
    "execution_count": 11,
    "metadata": {
-    "collapsed": false,
-    "deletable": true,
-    "editable": true,
     "slideshow": {
      "slide_type": "subslide"
     }
@@ -681,9 +631,6 @@
    "cell_type": "code",
    "execution_count": 12,
    "metadata": {
-    "collapsed": false,
-    "deletable": true,
-    "editable": true,
     "slideshow": {
      "slide_type": "subslide"
     }
@@ -708,9 +655,6 @@
    "cell_type": "code",
    "execution_count": 13,
    "metadata": {
-    "collapsed": false,
-    "deletable": true,
-    "editable": true,
     "slideshow": {
      "slide_type": "-"
     }
@@ -734,9 +678,7 @@
   {
    "cell_type": "code",
    "execution_count": 18,
-   "metadata": {
-    "collapsed": false
-   },
+   "metadata": {},
    "outputs": [
     {
      "data": {
@@ -776,9 +718,9 @@
  "metadata": {
   "celltoolbar": "Slideshow",
   "kernelspec": {
-   "display_name": "pydelta-next",
+   "display_name": "Python 3",
    "language": "python",
-   "name": "pydelta-next"
+   "name": "python3"
   },
   "language_info": {
    "codemirror_mode": {
@@ -790,7 +732,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.4.6"
+   "version": "3.6.1"
   }
  },
  "nbformat": 4,
diff --git a/delta/deltas.py b/delta/deltas.py
index 5070804..7cb01b2 100644
--- a/delta/deltas.py
+++ b/delta/deltas.py
@@ -586,7 +586,7 @@ def __call__(self, corpus):
         dm = pairwise_distances(corpus, metric=self.metric, n_jobs=-1, **self.kwargs)
         if self.fix_symmetry:
             dm = np.tril(dm, -1)
-            dm += dm.T
+            dm = dm + dm.T
         df = pd.DataFrame(data=dm, index=corpus.index, columns=corpus.index)
         if self.scale:
             df = df / corpus.columns.size