diff --git a/gluturtle.cabal b/gluturtle.cabal
--- a/gluturtle.cabal
+++ b/gluturtle.cabal
@@ -2,7 +2,7 @@
 cabal-version:	>= 1.6
 
 name:		gluturtle
-version:	0.0.35
+version:	0.0.36
 stability:	alpha
 author:		Yoshikuni Jujo <PAF01143@nifty.ne.jp>
 maintainer:	Yoshikuni Jujo <PAF01143@nifty.ne.jp>
diff --git a/src/Graphics/UI/GLUT/Turtle/Field.hs b/src/Graphics/UI/GLUT/Turtle/Field.hs
--- a/src/Graphics/UI/GLUT/Turtle/Field.hs
+++ b/src/Graphics/UI/GLUT/Turtle/Field.hs
@@ -192,6 +192,7 @@
 	atomicModifyIORef_ (fActions f) (Just (makeLineAction f w c p q) :)
 
 makePolygonAction :: Field -> [Position] -> Color -> Color -> Double -> IO ()
+makePolygonAction _ [] _ _ _ = error "makePolygonAction: no points"
 makePolygonAction f ps c lc lw = do
 	ps' <- mapM (positionToDoubles f) ps
 	drawPolygon ps' (colorToInts c) (colorToInts lc) lw
diff --git a/src/Graphics/UI/GLUT/Turtle/GLUTools.hs b/src/Graphics/UI/GLUT/Turtle/GLUTools.hs
--- a/src/Graphics/UI/GLUT/Turtle/GLUTools.hs
+++ b/src/Graphics/UI/GLUT/Turtle/GLUTools.hs
@@ -169,6 +169,7 @@
 
 drawPolygon_ :: [G.Vertex3 G.GLfloat] -> G.Color4 G.GLfloat -> G.Color4 G.GLfloat ->
 	G.GLfloat -> IO ()
+drawPolygon_ [] _ _ _ = error "bad polygon"
 drawPolygon_ ps c lc lw = G.preservingMatrix $ do
 	G.color c
 	G.renderPrimitive G.Triangles $ mapM_ G.vertex ps'