diff --git a/qiskit/tools/visualization/_counts_visualization.py b/qiskit/tools/visualization/_counts_visualization.py
index 4a88037de0f7..8e8397ee8302 100644
--- a/qiskit/tools/visualization/_counts_visualization.py
+++ b/qiskit/tools/visualization/_counts_visualization.py
@@ -20,7 +20,6 @@
 from ._error import VisualizationError
 
 
-
 def plot_histogram(data, number_to_keep=False, legend=None, options=None):
     """Plot a histogram of data.
 
diff --git a/qiskit/tools/visualization/_error.py b/qiskit/tools/visualization/_error.py
index 0de8b1bef7bb..21dcf7be1dbf 100644
--- a/qiskit/tools/visualization/_error.py
+++ b/qiskit/tools/visualization/_error.py
@@ -1,6 +1,15 @@
+# -*- coding: utf-8 -*-
+
+# Copyright 2018, IBM.
+#
+# This source code is licensed under the Apache License, Version 2.0 found in
+# the LICENSE.txt file in the root directory of this source tree.
+
+"""QISKit visualization error classes."""
+
 from qiskit import QISKitError
 
+
 class VisualizationError(QISKitError):
     """For visualization specific errors."""
     pass
-