diff --git a/lib/fugit/nat.rb b/lib/fugit/nat.rb
index 0b0969f..26a5376 100644
--- a/lib/fugit/nat.rb
+++ b/lib/fugit/nat.rb
@@ -642,7 +642,7 @@ def conflate(index, slot)
         to_a(a).concat(to_a(b))
       end
       def hour_range
-        m = (key == :hm && @_data1 == 0 && @_data0.match(/\A(\d+)-(\d+)\z/))
+        m = (key == :hm && @_data1 == 0 && @_data0.to_s.match(/\A(\d+)-(\d+)\z/))
         m ? [ m[1].to_i, m[2].to_i ] : nil
       end
     end