diff --git a/formatters.py b/formatters.py
index fc3bd4c..2a47649 100644
--- a/formatters.py
+++ b/formatters.py
@@ -62,7 +62,10 @@
             sum_res = sum([r[1] for r in results])
             mean = sum_res/len(results)
             sum_sq = sum([(r[1] - mean) ** 2 for r in results])
-            dev = math.sqrt(sum_sq / (len(results) - 1))
+            if len(results) > 1:
+                dev = math.sqrt(sum_sq / (len(results) - 1))
+            else:
+                dev = 0
             data[key] = (mean, dev)
         return data