@@ -993,6 +993,7 @@
         self._colormode = _CFG["colormode"]
         self._keys = []
         self.clear()
+        self._reverse_left_right = 1
         if sys.platform == 'darwin':
             # Force Turtle window to the front on OS X. This is needed because
             # the Turtle window will show behind the Terminal window when you
@@ -1090,6 +1091,8 @@
             self.mode("world")
         xspan = float(urx - llx)
         yspan = float(ury - lly)
+        if xspan * yspan < 0:
+            self._reverse_left_right = -1
         wx, wy = self._window_size()
         self.screensize(wx-20, wy-20)
         oldxscale, oldyscale = self.xscale, self.yscale
@@ -1674,7 +1677,7 @@
         >>> turtle.heading()
         337.0
         """
-        self._rotate(-angle)
+        self._rotate(-angle * self.screen._reverse_left_right)

     def left(self, angle):
         """Turn turtle left by angle units.
@@ -1695,7 +1698,7 @@
         >>> turtle.heading()
         67.0
         """
-        self._rotate(angle)
+        self._rotate(angle * self.screen._reverse_left_righ)

     def pos(self):
         """Return the turtle's current location (x,y), as a Vec2D-vector.