diff --git a/Data/GPS.hs b/Data/GPS.hs
--- a/Data/GPS.hs
+++ b/Data/GPS.hs
@@ -29,6 +29,7 @@
 	, west
 	, radiusOfEarth
 	-- * Helper Functions
+	, heading
 	, restLocations
 	, closestDistance
 	, getRadianPair
@@ -47,7 +48,7 @@
 
 import Data.Time
 import Data.Maybe (listToMaybe)
-import Data.Fixed (mod')
+import Data.Fixed
 
 -- |Distances are expressed in meters
 type Distance = Double
@@ -75,6 +76,7 @@
   (lat1, lon1) = getRadianPairD a
   (lat2, lon2) = getRadianPairD b
 
+-- | Direction two points aim toward (0 = North, pi/2 = West, pi = South, 3pi/2 = East)
 heading         :: (Lat a, Lon a) => a -> a -> Heading	-- ^ 0 = North, pi/2 = West...
 heading a b =
 	atan2	(sin (diffLon) * cos (lat2)) 
@@ -220,7 +222,7 @@
 	in case first of
 		Nothing -> []
 		Just f  ->
-	    	     let sorted = sortBy (comparing ((`mod'` (2*pi)). (+ pi/2). heading f)) (filter (/= f) xs)
+	    	     let sorted = sortBy (comparing (eastZeroHeading f)) (filter (/= f) xs)
 		     in case sorted of
 			(a:b:cs) -> grahamScan (b:a:f:[]) cs
 			cs       -> f : cs
@@ -234,16 +236,17 @@
 		Straight  -> grahamScan (x:p2:p1:ps) xs
 		_	  -> grahamScan (p1:ps) (x:xs)
 
+eastZeroHeading :: (Lat c, Lon c) => c -> c -> Heading
+eastZeroHeading s = (`mod'` (2*pi)) . (+ pi/2) . heading s
+
 data Turn = LeftTurn | RightTurn | Straight deriving (Eq, Ord, Show, Read, Enum)
 
 turn :: (Lat c, Lon c) => c -> c -> c -> Turn
 turn a b c =
-	let h1 = heading a b
-	    h2 = heading b c
-	in case compare (h2 - h1) 0 of
-			LT -> RightTurn
-			GT -> LeftTurn
-			EQ -> Straight
+	let h1 = eastZeroHeading a b
+	    h2 = eastZeroHeading b c
+	    d  = h2 - h1
+	in if d >= 0 && d < pi then LeftTurn else RightTurn
 
 -- | Find the southmost point
 southMost :: (Lat c) => [c] -> Maybe c
diff --git a/gps.cabal b/gps.cabal
--- a/gps.cabal
+++ b/gps.cabal
@@ -1,5 +1,5 @@
 name:		gps
-version:	0.5.2
+version:	0.5.3
 license:	BSD3
 license-file:	LICENSE
 author:		Thomas DuBuisson <thomas.dubuisson@gmail.com>