diff --git a/src/sl/company_sl.cpp b/src/sl/company_sl.cpp
index 8360a94508..34023f5ec8 100644
--- a/src/sl/company_sl.cpp
+++ b/src/sl/company_sl.cpp
@@ -491,7 +491,7 @@ static void Save_PLYR()
 {
 	for (Company *c : Company::Iterate()) {
 		SlSetArrayIndex(c->index);
-		SlAutolength((AutolengthProc*)SaveLoad_PLYR, c);
+		SlAutolength(SaveLoad_PLYR, c);
 	}
 }
 
diff --git a/src/sl/linkgraph_sl.cpp b/src/sl/linkgraph_sl.cpp
index ce5830b6e7..ac781c4a7b 100644
--- a/src/sl/linkgraph_sl.cpp
+++ b/src/sl/linkgraph_sl.cpp
@@ -336,7 +336,7 @@ static void Save_LGRP()
 	FilterDescs();
 	for (LinkGraph *lg : LinkGraph::Iterate()) {
 		SlSetArrayIndex(lg->index);
-		SlAutolength((AutolengthProc*)DoSave_LGRP, lg);
+		SlAutolength(DoSave_LGRP, lg);
 	}
 }
 
@@ -348,7 +348,7 @@ static void Save_LGRJ()
 	FilterDescs();
 	for (LinkGraphJob *lgj : LinkGraphJob::Iterate()) {
 		SlSetArrayIndex(lgj->index);
-		SlAutolength((AutolengthProc*)DoSave_LGRJ, lgj);
+		SlAutolength(DoSave_LGRJ, lgj);
 	}
 }
 
diff --git a/src/sl/order_sl.cpp b/src/sl/order_sl.cpp
index f1ad9a8230..7c2af243d0 100644
--- a/src/sl/order_sl.cpp
+++ b/src/sl/order_sl.cpp
@@ -364,14 +364,13 @@ static void Save_ORDL()
 	SetupDescs_ORDL();
 	for (OrderList *list : OrderList::Iterate()) {
 		SlSetArrayIndex(list->index);
-		SlAutolength([](void *data) {
-			OrderList *list = static_cast<OrderList *>(data);
+		SlAutolength([&]() {
 			SlObjectSaveFiltered(list, _filtered_ordl_desc);
 			SlWriteUint32(list->GetScheduledDispatchScheduleCount());
 			for (DispatchSchedule &ds : list->GetScheduledDispatchScheduleSet()) {
 				SaveDispatchSchedule(ds);
 			}
-		}, list);
+		});
 	}
 }
 
@@ -458,14 +457,13 @@ void Save_BKOR()
 
 	for (OrderBackup *ob : OrderBackup::Iterate()) {
 		SlSetArrayIndex(ob->index);
-		SlAutolength([](void *data) {
-			OrderBackup *ob = static_cast<OrderBackup *>(data);
+		SlAutolength([&]() {
 			SlObject(ob, GetOrderBackupDescription());
 			SlWriteUint32((uint)ob->dispatch_schedules.size());
 			for (DispatchSchedule &ds : ob->dispatch_schedules) {
 				SaveDispatchSchedule(ds);
 			}
-		}, ob);
+		});
 	}
 }
 
diff --git a/src/sl/plans_sl.cpp b/src/sl/plans_sl.cpp
index 89e83dd07e..f3544b4839 100644
--- a/src/sl/plans_sl.cpp
+++ b/src/sl/plans_sl.cpp
@@ -40,7 +40,7 @@ static void Save_PLAN()
 {
 	for (Plan *p : Plan::Iterate()) {
 		SlSetArrayIndex(p->index);
-		SlAutolength((AutolengthProc*) RealSave_PLAN, p);
+		SlAutolength(RealSave_PLAN, p);
 	}
 }
 
diff --git a/src/sl/saveload.cpp b/src/sl/saveload.cpp
index d96f92e8f1..1ad1459931 100644
--- a/src/sl/saveload.cpp
+++ b/src/sl/saveload.cpp
@@ -2383,19 +2383,17 @@ void SlGlobList(const SaveLoadTable &slt)
 	SlObject(nullptr, slt);
 }
 
-/**
- * Do something of which I have no idea what it is :P
- * @param proc The callback procedure that is called
- * @param arg The variable that will be used for the callback procedure
- */
-void SlAutolength(AutolengthProc *proc, void *arg)
+void SlAutolengthSetup()
 {
 	assert(_sl.action == SLA_SAVE);
 	assert(_sl.need_length == NL_WANTLENGTH);
 
 	_sl.need_length = NL_NONE;
 	_sl.dumper->StartAutoLength();
-	proc(arg);
+}
+
+void SlAutolengthCompletion()
+{
 	auto result = _sl.dumper->StopAutoLength();
 	/* Setup length */
 	_sl.need_length = NL_WANTLENGTH;
diff --git a/src/sl/saveload.h b/src/sl/saveload.h
index b63d685fdf..18c3ae9097 100644
--- a/src/sl/saveload.h
+++ b/src/sl/saveload.h
@@ -83,7 +83,6 @@ bool IsNetworkServerSave();
 bool IsScenarioSave();
 
 typedef void ChunkSaveLoadProc();
-typedef void AutolengthProc(void *arg);
 
 void SlUnreachablePlaceholder();
 
@@ -980,12 +979,27 @@ void WriteValue(void *ptr, VarType conv, int64_t val);
 void SlSetArrayIndex(uint index);
 int SlIterateArray();
 
-void SlAutolength(AutolengthProc *proc, void *arg);
 size_t SlGetFieldLength();
 void SlSetLength(size_t length);
 size_t SlCalcObjMemberLength(const void *object, const SaveLoad &sld);
 size_t SlCalcObjLength(const void *object, const SaveLoadTable &slt);
 
+/**
+ * Run proc, automatically prepending the written length
+ * @param proc The callback procedure that is called
+ * @param args Any
+ */
+template <typename F, typename... Args>
+void SlAutolength(F proc, Args... args)
+{
+	extern void SlAutolengthSetup();
+	extern void SlAutolengthCompletion();
+
+	SlAutolengthSetup();
+	proc(std::forward<Args>(args)...);
+	SlAutolengthCompletion();
+}
+
 /**
  * Run proc, saving result in the autolength temp buffer
  * @param proc The callback procedure that is called
diff --git a/src/sl/station_sl.cpp b/src/sl/station_sl.cpp
index 7acb434382..1555acdb6e 100644
--- a/src/sl/station_sl.cpp
+++ b/src/sl/station_sl.cpp
@@ -622,7 +622,7 @@ static void Save_STNN()
 	/* Write the stations */
 	for (BaseStation *st : BaseStation::Iterate()) {
 		SlSetArrayIndex(st->index);
-		SlAutolength((AutolengthProc*)RealSave_STNN, st);
+		SlAutolength(RealSave_STNN, st);
 	}
 }
 
diff --git a/src/sl/town_sl.cpp b/src/sl/town_sl.cpp
index 754cbda0e7..008b4acd3f 100644
--- a/src/sl/town_sl.cpp
+++ b/src/sl/town_sl.cpp
@@ -317,7 +317,7 @@ static void Save_TOWN()
 	SetupDescs_TOWN();
 	for (Town *t : Town::Iterate()) {
 		SlSetArrayIndex(t->index);
-		SlAutolength((AutolengthProc*)RealSave_Town, t);
+		SlAutolength(RealSave_Town, t);
 	}
 }
 
diff --git a/src/sl/vehicle_sl.cpp b/src/sl/vehicle_sl.cpp
index 5e76094215..8885b129e2 100644
--- a/src/sl/vehicle_sl.cpp
+++ b/src/sl/vehicle_sl.cpp
@@ -1316,7 +1316,7 @@ void Save_VENC()
 		return;
 	}
 
-	SlAutolength([](void *) {
+	SlAutolength([]() {
 		int types[4] = {};
 		int total = 0;
 		for (Vehicle *v : Vehicle::Iterate()) {
@@ -1377,7 +1377,7 @@ void Save_VENC()
 			SlWriteUint32(a->index);
 			SlWriteUint16(a->acache.cached_max_range);
 		}
-	}, nullptr);
+	});
 }
 
 void Load_VENC()
@@ -1610,7 +1610,7 @@ void Save_VLKA()
 	for (Train *t : Train::Iterate()) {
 		if (t->lookahead != nullptr) {
 			SlSetArrayIndex(t->index);
-			SlAutolength((AutolengthProc*) RealSave_VLKA, t->lookahead.get());
+			SlAutolength(RealSave_VLKA, t->lookahead.get());
 		}
 	}
 }