--- a/src/Graphics.cc	Mon Dec 08 21:49:54 2008 +0000
+++ b/src/Graphics.cc	Mon Dec 08 21:54:04 2008 +0000
@@ -52,7 +52,10 @@
 }
 
 static PixelDimension value_between (PixelDimension low, PixelDimension value, PixelDimension high) {
-    if (value < low)
+    if (high < low)
+        return (high + low) / 2;
+
+    else if (value < low)
         return low;
 
     else if (value > high)