diff --git a/demo/moulinrouge/tests.py b/demo/moulinrouge/tests.py
index 87cdb50..ea9da49 100644
--- a/demo/moulinrouge/tests.py
+++ b/demo/moulinrouge/tests.py
@@ -517,6 +517,13 @@ def get_test_routes(app):
         pie.legend_at_bottom_columns = 4
         return pie.render_response()
 
+    @app.route('/test/interpolate/secondary')
+    def test_interpolate_secondary():
+        chart = Line(title=u'Some different points', interpolate='cubic')
+        chart.add('line', [1000, 2000, 7000])
+        chart.add('other line', [100, 500, 500], secondary=True)
+        return chart.render_response()
+
     @app.route('/test/legend_at_bottom/<chart>')
     def test_legend_at_bottom_for(chart):
         graph = CHARTS_BY_NAME[chart]()
diff --git a/pygal/graph/bar.py b/pygal/graph/bar.py
index 55b6680..5cf7543 100644
--- a/pygal/graph/bar.py
+++ b/pygal/graph/bar.py
@@ -61,9 +61,7 @@ class Bar(Graph):
         serie_node = self.svg.serie(serie)
         bars = self.svg.node(serie_node['plot'], class_="bars")
         if rescale and self.secondary_series:
-            points = [
-                (x, self._scale_diff + (y - self._scale_min_2nd) * self._scale)
-                for x, y in serie.points if y is not None]
+            points = self._rescale(serie.points)
         else:
             points = serie.points
 
diff --git a/pygal/graph/graph.py b/pygal/graph/graph.py
index 3578610..87cf6be 100644
--- a/pygal/graph/graph.py
+++ b/pygal/graph/graph.py
@@ -419,6 +419,11 @@ class Graph(BaseGraph):
             x, y, self.interpolation_precision,
             **self.interpolation_parameters))
 
+    def _rescale(self, points):
+        return [
+            (x, self._scale_diff + (y - self._scale_min_2nd) * self._scale)
+            for x, y in points if y is not None]
+
     def _tooltip_data(self, node, value, x, y, classes=None):
         self.svg.node(node, 'desc', class_="value").text = value
         if classes is None:
diff --git a/pygal/graph/line.py b/pygal/graph/line.py
index 65e92f2..fe16568 100644
--- a/pygal/graph/line.py
+++ b/pygal/graph/line.py
@@ -69,7 +69,11 @@ class Line(Graph):
                 if y is not None:
                     break
             else:
-                raise ValueError("Invalid value ({}) for config key 'missing_value_fill_truncation'; Use 'x', 'y' or 'either'".format(self.missing_value_fill_truncation))
+                raise ValueError(
+                    "Invalid value ({}) for config key "
+                    "'missing_value_fill_truncation';"
+                    " Use 'x', 'y' or 'either'".format(
+                        self.missing_value_fill_truncation))
             end -= 1
 
         return ([(values[0][0], zero)] +
@@ -80,9 +84,7 @@ class Line(Graph):
         """Draw the line serie"""
         serie_node = self.svg.serie(serie)
         if rescale and self.secondary_series:
-            points = [
-                (x, self._scale_diff + (y - self._scale_min_2nd) * self._scale)
-                for x, y in serie.points if y is not None]
+            points = self._rescale(serie.points)
         else:
             points = serie.points
         view_values = list(map(self.view, points))
@@ -118,7 +120,10 @@ class Line(Graph):
 
         if serie.stroke:
             if self.interpolate:
-                view_values = list(map(self.view, serie.interpolated))
+                points = serie.interpolated
+                if rescale and self.secondary_series:
+                    points = self._rescale(points)
+                view_values = list(map(self.view, points))
             if serie.fill:
                 view_values = self._fill(view_values)
             self.svg.line(