diff --git a/src/group_gui.cpp b/src/group_gui.cpp
--- a/src/group_gui.cpp
+++ b/src/group_gui.cpp
@@ -76,7 +76,7 @@ static void ShowGroupActionDropdown(Wind
 	list->push_back(new DropDownListStringItem(STR_SEND_FOR_SERVICING,  GALF_SERVICE, false));
 	list->push_back(new DropDownListStringItem(STR_SEND_TRAIN_TO_DEPOT, GALF_DEPOT,   false));
 
-	if (IsValidGroupID(gid)) {
+	if (Group::IsValidID(gid)) {
 		list->push_back(new DropDownListStringItem(STR_GROUP_ADD_SHARED_VEHICLE,  GALF_ADD_SHARED, false));
 		list->push_back(new DropDownListStringItem(STR_GROUP_REMOVE_ALL_VEHICLES, GALF_REMOVE_ALL, false));
 	}
@@ -321,7 +321,7 @@ public:
 			this->groups.ForceResort();
 		}
 
-		if (!(IsAllGroupID(this->group_sel) || IsDefaultGroupID(this->group_sel) || IsValidGroupID(this->group_sel))) {
+		if (!(IsAllGroupID(this->group_sel) || IsDefaultGroupID(this->group_sel) || Group::IsValidID(this->group_sel))) {
 			this->group_sel = ALL_GROUP;
 			HideDropDownMenu(this);
 		}
@@ -567,7 +567,7 @@ public:
 			}
 
 			case GRP_WIDGET_RENAME_GROUP: { // Rename the selected roup
-				assert(IsValidGroupID(this->group_sel));
+				assert(Group::IsValidID(this->group_sel));
 
 				const Group *g = Group::Get(this->group_sel);
 
@@ -595,7 +595,7 @@ public:
 			}
 
 			case GRP_WIDGET_REPLACE_PROTECTION:
-				if (IsValidGroupID(this->group_sel)) {
+				if (Group::IsValidID(this->group_sel)) {
 					const Group *g = Group::Get(this->group_sel);
 
 					DoCommandP(0, this->group_sel, !g->replace_protection, CMD_SET_GROUP_REPLACE_PROTECTION);
@@ -703,12 +703,12 @@ public:
 									| DEPOT_MASS_SEND, GetCmdSendToDepot(this->vehicle_type));
 						break;
 					case GALF_ADD_SHARED: // Add shared Vehicles
-						assert(IsValidGroupID(this->group_sel));
+						assert(Group::IsValidID(this->group_sel));
 
 						DoCommandP(0, this->group_sel, this->vehicle_type, CMD_ADD_SHARED_VEHICLE_GROUP | CMD_MSG(STR_GROUP_CAN_T_ADD_SHARED_VEHICLE));
 						break;
 					case GALF_REMOVE_ALL: // Remove all Vehicles from the selected group
-						assert(IsValidGroupID(this->group_sel));
+						assert(Group::IsValidID(this->group_sel));
 
 						DoCommandP(0, this->group_sel, this->vehicle_type, CMD_REMOVE_ALL_VEHICLES_GROUP | CMD_MSG(STR_GROUP_CAN_T_REMOVE_ALL_VEHICLES));
 						break;
@@ -758,7 +758,7 @@ static WindowDesc _group_desc(
 
 void ShowCompanyGroup(CompanyID company, VehicleType vehicle_type)
 {
-	if (!IsValidCompanyID(company)) return;
+	if (!Company::IsValidID(company)) return;
 
 	_group_desc.cls = GetWindowClassForVehicleType(vehicle_type);
 	WindowNumber num = (vehicle_type << 11) | VLW_GROUP_LIST | company;