diff --git a/lib/histogram.rb b/lib/histogram.rb
index eb095cb..546d3f1 100644
--- a/lib/histogram.rb
+++ b/lib/histogram.rb
@@ -343,7 +343,7 @@ def histogram(*args)
           if index == bins
             index -= 1
           end
-          _freqs[index] += height
+          _freqs[index] += height if _freqs[index]
         end
         _freqs
       end