diff --git a/Diagram.hs b/Diagram.hs
index 8e02d72..874aa2d 100644
--- a/Diagram.hs
+++ b/Diagram.hs
@@ -112,6 +112,7 @@ showConvexHullPoints = Diag f
 showConvexHullLines :: Diag
 showConvexHullLines = Diag f
   where
+    f _ [] = mempty
     f _ vt
       = (strokeTrail                       .
          fromVertices                      .