diff --git a/agda.rb b/agda.rb
index b188cfa..c0dfcad 100644
--- a/agda.rb
+++ b/agda.rb
@@ -117,6 +117,12 @@ class Handler
         last_line = last_line_attr.to_s.to_i
       end
 
+      if first_line and last_line
+        line_range = first_line..last_line
+      else
+        line_range = 1..
+      end
+
       full_path = t.attribute("data-file-path").to_s
       full_path_dirs = Pathname(full_path).each_filename.to_a
 
@@ -148,7 +154,7 @@ class Handler
       # of code output. We can iterate over these and match them up with
       # the line numbers we got from reading the Agda HTML output.
       lines = t.css("pre.chroma code[data-lang] .line")
-      lines.zip((first_line..last_line)).each do |line, line_no|
+      lines.zip(line_range).each do |line, line_no|
         line_info = agda_info[line_no]
         next unless line_info