diff --git a/src/box/lua/tuple.cc b/src/box/lua/tuple.cc
index b63e2b68fe6a98ed65595c0328aa14fb08c7df88..b872cce87ce6a31720a87e03808017cb98432742 100644
--- a/src/box/lua/tuple.cc
+++ b/src/box/lua/tuple.cc
@@ -574,6 +574,7 @@ box_lua_tuple_init(struct lua_State *L)
 	/* export C functions to Lua */
 	luaL_newmetatable(L, tuplelib_name);
 	luaL_register(L, NULL, lbox_tuple_meta);
+	/* save Lua/C functions to the global variable (cleaned by tuple.lua) */
 	lua_setglobal(L, "cfuncs");
 	luaL_register_type(L, tuple_iteratorlib_name,
 			   lbox_tuple_iterator_meta);
diff --git a/src/box/lua/tuple.lua b/src/box/lua/tuple.lua
index d81d24fe3f8f7f3372e8ce1d55026ecb9a30e5f8..c2989d2897f30f87076755eb5865330f158b7ae1 100644
--- a/src/box/lua/tuple.lua
+++ b/src/box/lua/tuple.lua
@@ -38,6 +38,8 @@ ffi.metatype('struct tuple', {
     __gc = tuple_gc;
     __len = cfuncs.__len;
     __tostring = function(tuple)
+        -- Unpack tuple, call yaml.encode, remove yaml header and footer
+        -- 5 = '---\n\n' (header), -6 = '\n...\n' (footer)
         return yaml.encode(methods.totable(tuple)):sub(5, -6)
     end;
     __index = function(tuple, key)