diff --git a/src/autoreplace_cmd.cpp b/src/autoreplace_cmd.cpp
index bb2cf0b02a..26a92e5197 100644
--- a/src/autoreplace_cmd.cpp
+++ b/src/autoreplace_cmd.cpp
@@ -50,9 +50,7 @@ static bool EnginesHaveCargoInCommon(EngineID engine_a, EngineID engine_b)
  */
 bool CheckAutoreplaceValidity(EngineID from, EngineID to, CompanyID company)
 {
-	/* First we make sure that it's a valid type the user requested
-	 * check that it's an engine that is in the engine array */
-	if (!Engine::IsValidID(from) || !Engine::IsValidID(to)) return false;
+	assert(Engine::IsValidID(from) && Engine::IsValidID(to));
 
 	/* we can't replace an engine into itself (that would be autorenew) */
 	if (from == to) return false;
diff --git a/src/company_cmd.cpp b/src/company_cmd.cpp
index e968108ea3..dfe7478a69 100644
--- a/src/company_cmd.cpp
+++ b/src/company_cmd.cpp
@@ -663,7 +663,10 @@ CommandCost CmdSetAutoReplace(TileIndex tile, DoCommandFlag flags, uint32 p1, ui
 	CommandCost cost;
 
 	if (!Group::IsValidID(id_g) && !IsAllGroupID(id_g) && !IsDefaultGroupID(id_g)) return CMD_ERROR;
+	if (!Engine::IsValidID(old_engine_type)) return CMD_ERROR;
+
 	if (new_engine_type != INVALID_ENGINE) {
+		if (!Engine::IsValidID(new_engine_type)) return CMD_ERROR;
 		if (!CheckAutoreplaceValidity(old_engine_type, new_engine_type, _current_company)) return CMD_ERROR;
 
 		cost = AddEngineReplacementForCompany(c, old_engine_type, new_engine_type, id_g, flags);
@@ -671,7 +674,7 @@ CommandCost CmdSetAutoReplace(TileIndex tile, DoCommandFlag flags, uint32 p1, ui
 		cost = RemoveEngineReplacementForCompany(c, old_engine_type, id_g, flags);
 	}
 
-	if (IsLocalCompany()) InvalidateAutoreplaceWindow(old_engine_type, id_g);
+	if ((flags & DC_EXEC) && IsLocalCompany()) InvalidateAutoreplaceWindow(old_engine_type, id_g);
 
 	return cost;
 }