diff --git a/src/ai.cpp b/src/ai.cpp
index 05925183ed6..69fc2268f10 100644
--- a/src/ai.cpp
+++ b/src/ai.cpp
@@ -305,6 +305,7 @@ bool ai_interface::recruit(const std::string& unit_name, location loc)
 		" gold=" << data.gold <<
 		((data.net_income < 0) ? "" : "+") <<
 		data.net_income << "\n";
+		recorder.add_checksum_check(loc);
 		return true;
 	} else {
 		const team_data data = calculate_team_data(current_team(),info_.team_num,info_.units);
diff --git a/src/game.cpp b/src/game.cpp
index eab8c9f7aca..4693814b5fa 100644
--- a/src/game.cpp
+++ b/src/game.cpp
@@ -203,6 +203,7 @@ game_controller::game_controller(int argc, char** argv)
 			test_mode_ = true;
 		} else if(val == "--debug" || val == "-d") {
 			game_config::debug = true;
+			game_config::mp_debug = true;
 		} else if (val.substr(0, 6) == "--log-") {
 		} else if(val == "--nosound") {
 			preferences::set_sound(false);
diff --git a/src/game_config.cpp b/src/game_config.cpp
index b384c6abc68..878b8318d22 100644
--- a/src/game_config.cpp
+++ b/src/game_config.cpp
@@ -30,7 +30,7 @@ namespace game_config
 	int kill_experience = 8;
 	int leadership_bonus = 25;
 	const std::string version = VERSION;
-	bool debug = false, editor = false, ignore_replay_errors = false;
+	bool debug = false, editor = false, ignore_replay_errors = false, mp_debug = false;
 
 	std::string game_icon = "wesnoth-icon.png", game_title, game_logo, title_music, anonymous_music,
 			victory_music, defeat_music;
diff --git a/src/game_config.hpp b/src/game_config.hpp
index 984531b4c04..3ede0086982 100644
--- a/src/game_config.hpp
+++ b/src/game_config.hpp
@@ -33,7 +33,7 @@ namespace game_config
 	extern int leadership_bonus;
 	extern const std::string version;
 
-	extern bool debug, editor, ignore_replay_errors;
+	extern bool debug, editor, ignore_replay_errors, mp_debug;
 
 	extern std::string path;
 
diff --git a/src/menu_events.cpp b/src/menu_events.cpp
index 59b52296b70..a7859308f7a 100644
--- a/src/menu_events.cpp
+++ b/src/menu_events.cpp
@@ -644,6 +644,7 @@ namespace events{
 				gui_->recalculate_minimap();
 				gui_->invalidate_game_status();
 				gui_->invalidate_all();
+				recorder.add_checksum_check(loc);
 			} else {
 				recorder.undo();
 				gui::show_dialog(*gui_,NULL,"",msg,gui::OK_ONLY);
@@ -753,6 +754,7 @@ namespace events{
 						recall_list.erase(recall_list.begin()+res);
 						gui_->invalidate_game_status();
 						gui_->invalidate_all();
+						recorder.add_checksum_check(loc);
 					}
 				}
 			}
@@ -895,6 +897,7 @@ namespace events{
 
 					gui_->invalidate(action.recall_loc);
 					gui_->draw();
+					recorder.add_checksum_check(action.recall_loc);
 				} else {
 					recorder.undo();
 					gui::show_dialog(*gui_,NULL,"",msg,gui::OK_ONLY);
@@ -936,6 +939,7 @@ namespace events{
 				gui_->draw();
 				//gui_.invalidate_game_status();
 				//gui_.invalidate_all();
+				recorder.add_checksum_check(loc);
 			} else {
 				recorder.undo();
 				gui::show_dialog(*gui_,NULL,"",msg,gui::OK_ONLY);
diff --git a/src/replay.cpp b/src/replay.cpp
index 0ec17b472c4..885496c7613 100644
--- a/src/replay.cpp
+++ b/src/replay.cpp
@@ -214,6 +214,21 @@ void replay::save_game(const std::string& label, const config& snapshot,
 	saveInfo_.snapshot = config();
 }
 
+void replay::add_unit_checksum(const gamemap::location& loc,config* const cfg)
+{
+	if(! game_config::mp_debug) {
+		return;
+	}
+	wassert(unit_map_ref);
+	config& cc = cfg->add_child("checksum");
+	loc.write(cc);
+	unit_map::const_iterator u = unit_map_ref->find(loc);
+	wassert(u != unit_map_ref->end());
+	std::string chk_value;
+	u->second.write_checksum(chk_value);
+	cc["value"] = chk_value;
+}
+
 void replay::add_start()
 {
 	config* const cmd = add_command(true);
@@ -286,6 +301,8 @@ void replay::add_attack(const gamemap::location& a, const gamemap::location& b,
 	char buf[100];
 	snprintf(buf,sizeof(buf),"%d",weapon);
 	current_->child("attack")->values["weapon"] = buf;
+	add_unit_checksum(a,current_);
+	add_unit_checksum(b,current_);
 }
 
 void replay::add_pos(const std::string& type,
@@ -366,6 +383,14 @@ void replay::add_event(const std::string& name)
 	ev["raise"] = name;
 	(*cmd)["undo"] = "no";
 }
+void replay::add_checksum_check(const gamemap::location& loc)
+{
+	if(! game_config::mp_debug) {
+		return;
+	}
+	config* const cmd = add_command();
+	add_unit_checksum(loc,cmd);
+}
 void replay::speak(const config& cfg)
 {
 	config* const cmd = add_command(false);
@@ -560,6 +585,32 @@ replay& get_replay_source()
 	}
 }
 
+namespace {
+void check_checksums(display& disp,const unit_map& units,const config& cfg)
+{
+	if(! game_config::mp_debug) {
+		return;
+	}
+	for(config::child_list::const_iterator ci = cfg.get_children("checksum").begin(); ci != cfg.get_children("checksum").end(); ++ci) {
+		gamemap::location loc(**ci);
+		unit_map::const_iterator u = units.find(loc);
+		if(u == units.end()) {
+			std::stringstream message;
+			message << "non existant unit to checksum at " << loc.x+1 << "," << loc.y+1 << "!";
+			disp.add_chat_message("verification",1,message.str(),display::MESSAGE_PRIVATE);
+			continue;
+		}
+		std::string check;
+		u->second.write_checksum(check);
+		if(check != (**ci)["value"]) {
+			std::stringstream message;
+			message << "checksum mismatch at " << loc.x+1 << "," << loc.y+1 << "!";
+			disp.add_chat_message("verification",1,message.str(),display::MESSAGE_PRIVATE);
+		}
+	}
+}
+}
+
 bool do_replay(display& disp, const gamemap& map, const game_data& gameinfo,
                unit_map& units,
 	       std::vector<team>& teams, int team_num, const gamestatus& state,
@@ -618,7 +669,8 @@ bool do_replay(display& disp, const gamemap& map, const game_data& gameinfo,
 				continue;
 			}
 		}
-
+		
+		
 		//if there is nothing more in the records
 		if(cfg == NULL) {
 			//replayer.set_skip(false);
@@ -728,6 +780,7 @@ bool do_replay(display& disp, const gamemap& map, const game_data& gameinfo,
 			current_team.spend_gold(u_type->second.cost());
 			LOG_NW << "-> " << (current_team.gold()) << "\n";
 			fix_shroud = !replayer.is_skipping();
+			check_checksums(disp,units,*cfg);
 }
 
 		else if((child = cfg->child("recall")) != NULL) {
@@ -755,6 +808,7 @@ bool do_replay(display& disp, const gamemap& map, const game_data& gameinfo,
 				if (!game_config::ignore_replay_errors) throw replay::error();
 			}
 			fix_shroud = !replayer.is_skipping();
+			check_checksums(disp,units,*cfg);
 		}
 
 		else if((child = cfg->child("disband")) != NULL) {
@@ -852,6 +906,7 @@ bool do_replay(display& disp, const gamemap& map, const game_data& gameinfo,
 			up->first = dst;
 			units.add(up);
 			u = units.find(dst);
+			check_checksums(disp,units,*cfg);
 			if(map.is_village(dst)) {
 				const int orig_owner = village_owner(dst,teams) + 1;
 				if(orig_owner != team_num) {
@@ -883,6 +938,7 @@ bool do_replay(display& disp, const gamemap& map, const game_data& gameinfo,
 		else if((child = cfg->child("attack")) != NULL) {
 			const config* const destination = child->child("destination");
 			const config* const source = child->child("source");
+			check_checksums(disp,units,*cfg);
 
 			if(destination == NULL || source == NULL) {
 				ERR_NW << "no destination/source found in attack\n";
@@ -938,8 +994,12 @@ bool do_replay(display& disp, const gamemap& map, const game_data& gameinfo,
 			}
 			game_events::fire((*child)["raise"]);
 		} else {
-			ERR_NW << "unrecognized action\n";
-			if (!game_config::ignore_replay_errors) throw replay::error();
+			if(! cfg->child("checksum")) {
+				ERR_NW << "unrecognized action\n";
+				if (!game_config::ignore_replay_errors) throw replay::error();
+			} else {
+				check_checksums(disp,units,*cfg);
+			}
 		}
 
 		//Check if we should refresh the shroud, and redraw the minimap/map tiles.
diff --git a/src/replay.hpp b/src/replay.hpp
index 0c301dc639e..1ae8fa7c036 100644
--- a/src/replay.hpp
+++ b/src/replay.hpp
@@ -58,6 +58,8 @@ public:
 	void add_rename(const std::string& name, const gamemap::location& loc);
 	void end_turn();
 	void add_event(const std::string& name);
+	void add_unit_checksum(const gamemap::location& loc,config* const cfg);
+	void add_checksum_check(const gamemap::location& loc);
 
 	void speak(const config& cfg);
 	std::string build_chat_log(const std::string& team) const;
diff --git a/src/unit.cpp b/src/unit.cpp
index 92808e7d36d..ddb7c1c019e 100644
--- a/src/unit.cpp
+++ b/src/unit.cpp
@@ -203,7 +203,13 @@ void unit::set_game_context(const game_data* gamedata, unit_map* unitmap, const
 	gamestatus_ = game_status;
 	teams_ = teams;
 }
-
+void unit::write_checksum(std::string& str) const
+{
+	config unit_config;
+	write(unit_config);
+	unit_config["controller"] = "";
+	str = unit_config.hash();
+}
 
 std::string unit::generate_description() const
 {
@@ -932,7 +938,6 @@ void unit::read(const config& cfg)
 	
 	bool type_set = false;
 	id_ = "";
-	traits_description_ = cfg["traits_description"];
 	if(cfg["type"] != "" && cfg["type"] != cfg["id"]) {
 		wassert(gamedata_ != NULL);
 		std::map<std::string,unit_type>::const_iterator i = gamedata_->unit_types.find(cfg["type"]);
@@ -1159,8 +1164,6 @@ void unit::write(config& cfg) const
 	cfg["user_description"] = custom_unit_description_;
 	cfg["description"] = underlying_description_;
 
-	cfg["traits_description"] = traits_description_;
-
 	if(can_recruit())
 		cfg["canrecruit"] = "1";
 
diff --git a/src/unit.hpp b/src/unit.hpp
index 5aeeefcd043..f642733547e 100644
--- a/src/unit.hpp
+++ b/src/unit.hpp
@@ -59,6 +59,7 @@ class unit
 		virtual ~unit();
 		
 		void set_game_context(const game_data* gamedata, unit_map* unitmap, const gamemap* map, const gamestatus* game_status, const std::vector<team>* teams);
+		void write_checksum(std::string& str) const;
 		
 		// Advances this unit to another type
 		void advance_to(const unit_type* t);
diff --git a/src/unit_types.cpp b/src/unit_types.cpp
index 43740412b62..75016c73ac2 100644
--- a/src/unit_types.cpp
+++ b/src/unit_types.cpp
@@ -954,11 +954,11 @@ const std::string& unit_type::image_profile() const
 		return val;
 }
 
-const std::string& unit_type::unit_description() const
+const t_string& unit_type::unit_description() const
 {
-	static const std::string default_val("No description available");
+	static const t_string default_val("No description available");
 
-	const std::string& desc = cfg_["unit_description"];
+	const t_string& desc = cfg_["unit_description"];
 	if(desc.empty())
 		return default_val;
 	else
diff --git a/src/unit_types.hpp b/src/unit_types.hpp
index bcfea1ce4d5..386b8484b4f 100644
--- a/src/unit_types.hpp
+++ b/src/unit_types.hpp
@@ -188,7 +188,7 @@ public:
 	
 	const std::string& image() const;
 	const std::string& image_profile() const;
-	const std::string& unit_description() const;
+	const t_string& unit_description() const;
 
     const std::vector<Uint32>& flag_rgb() const;