diff --git a/lib/plot.py b/lib/plot.py
index 5ee70c5..f1808a3 100644
--- a/lib/plot.py
+++ b/lib/plot.py
@@ -179,6 +179,7 @@ class SVGPlotter(Plotter):
         self.context.scale(dpi / 25.4, dpi / 25.4)
         self.context.set_line_cap(cairo.LINE_CAP_ROUND)
         self.context.set_line_join(cairo.LINE_JOIN_ROUND)
+        self.context.set_operator(cairo.OPERATOR_MULTIPLY)
 
         super().__init__(paper, line_width, colour)