diff --git a/genstar/Main.hs b/genstar/Main.hs
index a948d3b..9bccc41 100644
--- a/genstar/Main.hs
+++ b/genstar/Main.hs
@@ -44,18 +44,20 @@ instance Show PolygonPath where
   show (PolygonPath []) = ""
 
 -- | 'regularPolygonMod' @n@ @rf@ @pos@
--- creates a regular @n@-gon
+-- creates a regular @n@-gon (@n@ must be greater than or equal to 3)
 -- with the centre at @pos@
 -- that is modified in the sense that it takes @rf@,
 -- which is used to set the radius for each individual point.
-regularPolygonMod :: Integer -> (Integer -> Double) -> Vertex -> PolygonPath
-regularPolygonMod n rf pos = PolygonPath (map (\step -> move pos $ scale (rf step) $ fromAngle (fromInteger step * 2 * pi / fromInteger n)) [0 .. (n - 1)])
+regularPolygonMod :: Integer -> (Integer -> Double) -> Vertex -> Maybe PolygonPath
+regularPolygonMod n rf pos
+  | n < 3 = Nothing
+  | otherwise = Just (PolygonPath (map (\step -> move pos $ scale (rf step) $ fromAngle (fromInteger step * 2 * pi / fromInteger n)) [0 .. (n - 1)]))
 
 -- | 'regularPolygon' @n@ @r@ @pos@
 -- creates a regular polygon
 -- with the radius @r@
 -- and the centre at @pos@.
-regularPolygon :: Integer -> Double -> Vertex -> PolygonPath
+regularPolygon :: Integer -> Double -> Vertex -> Maybe PolygonPath
 regularPolygon n r = regularPolygonMod n (const r)
 
 -- | 'star' @n@ @r1@ @r2@ @pos@
@@ -64,7 +66,7 @@ regularPolygon n r = regularPolygonMod n (const r)
 -- the inner radius @r1@,
 -- the outer radius @r2@
 -- and the centre @pos@.
-star :: Integer -> Double -> Double -> Vertex -> PolygonPath
+star :: Integer -> Double -> Double -> Vertex -> Maybe PolygonPath
 star n r1 r2 = regularPolygonMod (n * 2) ((take (fromInteger n * 2) (cycle [r1, r2]) !!) . fromInteger)
 
 main :: IO ()