diff --git a/src/bitrot.py b/src/bitrot.py
index 97fe219..4275b99 100644
--- a/src/bitrot.py
+++ b/src/bitrot.py
@@ -112,7 +112,7 @@ def run(verbosity=1, test=False):
         new_mtime = int(st.st_mtime)
         current_size += st.st_size
         if verbosity:
-            size_fmt = '\r{:>6.1%}'.format(current_size/total_size)
+            size_fmt = '\r{:>6.1%}'.format(current_size/total_size if total_size > 0 else 0)
             if size_fmt != last_reported_size:
                 sys.stdout.write(size_fmt)
                 sys.stdout.flush()