diff --git a/lib/github/markup/command_implementation.rb b/lib/github/markup/command_implementation.rb
index 4ecf2ad5..b58d3261 100644
--- a/lib/github/markup/command_implementation.rb
+++ b/lib/github/markup/command_implementation.rb
@@ -53,11 +53,13 @@ def execute(command, target)
           output = Open3.popen3(*command) do |stdin, stdout, stderr, wait_thr|
             stdin.puts target
             stdin.close
-            if wait_thr.value.success?
-              stdout.readlines
-            else
-              raise CommandError.new(stderr.readlines.join('').strip)
-            end
+
+            stdout_lines = stdout.readlines
+            stderr_lines = stderr.readlines.join('').strip
+
+            raise CommandError.new(stderr_lines) unless wait_thr.value.success?
+
+            stdout_lines
           end
           sanitize(output.join(''), target.encoding)
         end