--- a/mercurial/cmdutil.py
+++ b/mercurial/cmdutil.py
@@ -160,9 +160,11 @@ def findrenames(repo, added=None, remove
                 for line in alines[x1:x2]:
                     equal += len(line)
 
-            myscore = equal*2.0 / (len(aa)+len(rr))
-            if myscore >= bestscore:
-                bestname, bestscore = r, myscore
+            lengths = len(aa) + len(rr)
+            if lengths:
+                myscore = equal*2.0 / lengths
+                if myscore >= bestscore:
+                    bestname, bestscore = r, myscore
         if bestname:
             yield bestname, a, bestscore