diff --git a/lib/method_source/code_helpers.rb b/lib/method_source/code_helpers.rb
index 4185c18..632d175 100644
--- a/lib/method_source/code_helpers.rb
+++ b/lib/method_source/code_helpers.rb
@@ -52,7 +52,7 @@ def expression_at(file, line_number, options={})
     def comment_describing(file, line_number)
       lines = file.is_a?(Array) ? file : file.each_line.to_a
 
-      extract_last_comment(lines[0..(line_number - 2)])
+      extract_last_comment(lines[0, line_number - 1])
     end
 
     # Determine if a string of code is a complete Ruby expression.
diff --git a/spec/method_source/code_helpers_spec.rb b/spec/method_source/code_helpers_spec.rb
index 287ff89..4db16b6 100644
--- a/spec/method_source/code_helpers_spec.rb
+++ b/spec/method_source/code_helpers_spec.rb
@@ -5,6 +5,11 @@
     @tester = Object.new.extend(MethodSource::CodeHelpers)
   end
 
+  it "does not read trailing comments for a first-line expression" do
+    lines = ["def first; end\n", "# unrelated tail\n"]
+    expect(@tester.comment_describing(lines, 1)).to eq("")
+  end
+
   [
     ["p = '", "'"],
     ["def", "a", "(); end"],