diff --git a/changes.txt b/changes.txt
--- a/changes.txt
+++ b/changes.txt
@@ -1,3 +1,9 @@
+0.4.0.0
+-------
+
+- fixes "third quadrant" bug.
+- Released Sun 10 Nov 2019 19:14:01 CET.
+
 0.3.0.0
 -------
 
diff --git a/line-drawing.cabal b/line-drawing.cabal
--- a/line-drawing.cabal
+++ b/line-drawing.cabal
@@ -1,6 +1,6 @@
 cabal-version:       >=1.10
 name:                line-drawing
-version:             0.3.0.0
+version:             0.4.0.0
 synopsis:            raster line drawing
 description:         Line drawing algorithms to approximate a
                      line segment on discrete graphical media (raster).
@@ -30,6 +30,7 @@
   main-is:             Test.hs
   build-depends:       base == 4.*
                        , hspec == 2.7.*
+                       , QuickCheck == 2.13.*
   other-modules:       Line.Draw
                        Line.DrawSpec
   type:                exitcode-stdio-1.0
diff --git a/src/Line/Draw.hs b/src/Line/Draw.hs
--- a/src/Line/Draw.hs
+++ b/src/Line/Draw.hs
@@ -37,21 +37,23 @@
             | m1Check   = bresenhamBase x y
             | otherwise = let x' = T.swap x
                               y' = T.swap y
-                          in map (T.swap) (bresenhamBase x' y')
+                          in map T.swap (bresenhamBase x' y')
     where
           m1Check :: Bool
-          m1Check = abs (x2 - x1) >= abs (y2 - y1)
+          m1Check = abs (x2 - x1) > abs (y2 - y1)
 
 
 -----------------
 -- ANCILLARIES --
 -----------------
 
+-- bresenhamBase is only valid when y-distance is greater than x-one
 bresenhamBase :: forall a . Integral a => (a, a) -> (a, a) -> [(a, a)]
 bresenhamBase (x1, y1) (x2, y2) =
         let -- first treshold
             ti = 2 * ady - adx
         in L.unfoldr f (x1, y1, ti)
+           -- unfoldr :: (b -> Maybe (a, b)) -> b -> [a]
     where
           -- slope
           dx, dy, adx, ady :: a
@@ -63,23 +65,27 @@
           -- sign of increment
           ix, iy :: a -> a
           ix | dx > 0    = (+1)
-             | otherwise = (subtract 1)
+             | otherwise = subtract 1
           iy | dy > 0    = (+1)
-             | otherwise = (subtract 1)
+             | otherwise = subtract 1
 
           -- step function, takes (x, y, treshold)
-                -- type State  = (Int, Int, Int)
                 -- curr x, curr y, treshold
           f :: (a, a, a) -> Maybe ((a, a), (a, a, a))
-          f (cx, cy, t)
-              | abs cx > abs x2 = Nothing
+          f (wx, wy, t)
+                    -- pos dx and neg dx have different reach conditions
+                    -- can't use abs wx > abs x2
+              | dx >= 0 &&
+                wx > x2         = Nothing
+              | dx <  0 &&
+                wx < x2         = Nothing
               | otherwise       =
-                    let cx' = ix cx
+                    let wx' = ix wx
 
-                        cy' | t > 0     = iy cy
-                            | otherwise = cy
+                        wy' | t > 0     = iy wy
+                            | otherwise = wy
 
                         t' | t > 0     = t - 2 * adx + 2 * ady
                            | otherwise = t + 2 * ady
-                    in Just ((cx, cy), (cx', cy', t'))
+                    in Just ((wx, wy), (wx', wy', t'))
 
diff --git a/test/Line/DrawSpec.hs b/test/Line/DrawSpec.hs
--- a/test/Line/DrawSpec.hs
+++ b/test/Line/DrawSpec.hs
@@ -3,6 +3,7 @@
 import Line.Draw
 
 import Test.Hspec
+import Test.QuickCheck
 
 
 main :: IO ()
@@ -11,7 +12,7 @@
 spec :: Spec
 spec = do
 
-  describe "bresenham" $ do
+  describe "bresenham (hspec)" $ do
     it "rasterises a simple line" $
       bresenham (0 :: Int, 0) (4, 4) `shouldBe`
         [(0,0), (1,1), (2,2), (3,3), (4,4)]
@@ -36,4 +37,13 @@
     it "returns a singleton list if start and end are the same" $
       bresenham (2 :: Int, 2) (2, 2) `shouldBe`
         [(2,2)]
+    it "does not get confused with points on second quadrant" $
+      bresenham (13 :: Int, 17) (12, 18) `shouldBe`
+        [(13,17), (12,18)]
 
+  describe "bresenham (quickcheck)" $ do
+    it "does never return an empty list" $ property $
+      \(p1, p2) -> length (bresenham (p1 :: (Int, Int)) p2) /= 0
+    it "is the same length with args flipped" $ property $
+      \(p1, p2) -> length (bresenham (p1 :: (Int, Int)) p2) ==
+                   length (bresenham p2                 p1)