diff --git a/buffer.py b/buffer.py
index 6718f95..32f6fe5 100644
--- a/buffer.py
+++ b/buffer.py
@@ -523,15 +523,19 @@ class Binary32Buffer(FileBuffer):
     def __init__(self, path, nl='\n', name=None):
         '''fb = FileBuffer(path)'''
         FileBuffer.__init__(self, path, nl, name)
-    def cursorx_to_datax(self, cx):
+    def cursorx_to_datax(self, cy, cx):
         if cx >= 0 and cx < 8:
-            return cx // 2
+            ix = cx // 2
         elif cx >= 9 and cx < 17:
-            return (cx - 1) // 2
+            ix = (cx - 1) // 2
         elif cx >= 18 and cx < 26:
-            return (cx - 2) // 2
+            ix = (cx - 2) // 2
         elif cx >= 27 and cx < 35:
-            return (cx - 3) // 2
+            ix = (cx - 3) // 2
+        else:
+            return None
+        if ix < len(self.rawdata[cy]):
+            return ix
         else:
             return None
     def datax_to_cursorx(self, ix):
@@ -546,7 +550,7 @@ class Binary32Buffer(FileBuffer):
         else:
             return None
     def overwrite_char(self, p, c, act=ACT_NORM, force=False):
-        ix = self.cursorx_to_datax(p.x)
+        ix = self.cursorx_to_datax(p.y, p.x)
         if ix is None:
             return
         Buffer.overwrite_char(self, p, c, act, force)
diff --git a/mode/hex.py b/mode/hex.py
index bdd1e1e..e86c25b 100644
--- a/mode/hex.py
+++ b/mode/hex.py
@@ -50,7 +50,8 @@ class Hex(mode.Fundamental):
             (cx, cy) = self.window.cursor.xy()
             s = string.translate(self.window.buffer.rawdata[y], self.ctrans)
             if cy == y:
-                i = self.window.buffer.cursorx_to_datax(cx)
+                i = self.window.buffer.cursorx_to_datax(cy, cx)
+                
                 if i is None:
                     return ((0, s, color.build('green', 'default', 'bold')),)
                 elif i < len(s) - 1: