diff --git a/scripts/update_payload/checker.py b/scripts/update_payload/checker.py
index 549ffcb..8a86619 100644
--- a/scripts/update_payload/checker.py
+++ b/scripts/update_payload/checker.py
@@ -67,7 +67,11 @@
   Returns:
     A string 'x (y)' where x = str(value) and y = format_func(value).
   """
-  return '%s (%s)' % (value, format_func(value))
+  ret = str(value)
+  formatted_str = format_func(value)
+  if formatted_str:
+    ret += ' (%s)' % formatted_str
+  return ret
 
 
 def _AddHumanReadableSize(size):
diff --git a/scripts/update_payload/format_utils.py b/scripts/update_payload/format_utils.py
index 2c82f32..2c3775c 100644
--- a/scripts/update_payload/format_utils.py
+++ b/scripts/update_payload/format_utils.py
@@ -27,9 +27,13 @@
     min_precision: minimum precision for fractional percentage
     max_precision: maximum precision for fractional percentage
   Returns:
-    Percentage string.
+    Percentage string, or None if percent cannot be computed (i.e. total is
+    zero).
 
   """
+  if total == 0:
+    return None
+
   percent = 0
   precision = min(min_precision, max_precision)
   factor = 10 ** precision
diff --git a/scripts/update_payload/histogram.py b/scripts/update_payload/histogram.py
index a5ddac4..9916329 100644
--- a/scripts/update_payload/histogram.py
+++ b/scripts/update_payload/histogram.py
@@ -101,11 +101,13 @@
         bar_len = count * self.scale / self.total
         hist_bar = '|%s|' % ('#' * bar_len).ljust(self.scale)
 
-      line = '%s %s %s (%s)' % (
+      line = '%s %s %s' % (
           str(key).ljust(self.max_key_len),
           hist_bar,
-          self.formatter(count),
-          format_utils.NumToPercent(count, self.total))
+          self.formatter(count))
+      percent_str = format_utils.NumToPercent(count, self.total)
+      if percent_str:
+        line += ' (%s)' % percent_str
       hist_lines.append(line)
 
     return '\n'.join(hist_lines)