diff --git a/command_table.hpp b/command_table.hpp
index 7a6ee81..85d7c3e 100644
--- a/command_table.hpp
+++ b/command_table.hpp
@@ -34,7 +34,7 @@
  * command is returned as a vector.
  */
 using CommandFunctor = std::function<std::vector<uint8_t>(
-                           std::vector<uint8_t>&, const message::Handler&)>;
+        const std::vector<uint8_t>&, const message::Handler&)>;
 
 /*
  * @struct CmdDetails