diff --git a/monitoring/histogram.cc b/monitoring/histogram.cc
index d2b7ff844..4970df7bd 100644
--- a/monitoring/histogram.cc
+++ b/monitoring/histogram.cc
@@ -202,6 +202,7 @@ std::string HistogramStat::ToString() const {
            Percentile(99.99));
   r.append(buf);
   r.append("------------------------------------------------------\n");
+  if (cur_num == 0) return r;   // all buckets are empty
   const double mult = 100.0 / cur_num;
   uint64_t cumulative_sum = 0;
   for (unsigned int b = 0; b < num_buckets_; b++) {