diff --git a/lib/fugit/parse.rb b/lib/fugit/parse.rb
index ee07b21..4acdff2 100644
--- a/lib/fugit/parse.rb
+++ b/lib/fugit/parse.rb
@@ -68,6 +68,7 @@ def do_parse_cronish(s, opts={})
     def parse_max(s, opts={})
 
       s0 = s.lines.first
+      return nil unless s0
 
       (0..[ ::Fugit::Nat::MAX_INPUT_LENGTH, s0.length - 1 ].min).each do |i|