diff --git a/src/kernel/turtle/Turtle.hx b/src/kernel/turtle/Turtle.hx
index 31ca387..42e8dc8 100644
--- a/src/kernel/turtle/Turtle.hx
+++ b/src/kernel/turtle/Turtle.hx
@@ -119,23 +119,17 @@ class Turtle {
 	}
 
 	public static function selectSlot(slot:TurtleSlot):Outcome<Noise, Noise> {
-		// TODO: slot in bounds?
-
-		var r = cc.Turtle.select(slot + 1);
+		var r = cc.Turtle.select(slot.toCCSlot());
 
 		return (r) ? Outcome.Success(null) : Outcome.Failure("Slot out of bounds");
 	}
 
 	public static function getItemCount(?slot:TurtleSlot):Int {
-		// TODO: slot in bounds?
-
-		return cc.Turtle.getItemCount(slot + 1);
+		return cc.Turtle.getItemCount(slot.toCCSlot());
 	}
 
 	public static function getItemSpace(?slot:TurtleSlot):Int {
-		// TODO: slot in bounds?
-
-		return cc.Turtle.getItemSpace(slot + 1);
+		return cc.Turtle.getItemSpace(slot.toCCSlot());
 	}
 
 	public static function detect(dir:InteractDirections):Bool {
@@ -208,12 +202,12 @@ class Turtle {
 	}
 
 	public static function compareSlot(otherSlot:TurtleSlot):Bool {
-		return cc.Turtle.compareTo(otherSlot + 1);
+		return cc.Turtle.compareTo(otherSlot.toCCSlot());
 	}
 
 	public static function transfer(from:TurtleSlot, to:TurtleSlot, ?count:Int):Outcome<Noise, Noise> {
 		selectSlot(from);
-		var r = cc.Turtle.transferTo(to + 1, count);
+		var r = cc.Turtle.transferTo(to.toCCSlot(), count);
 		return r ? Outcome.Success(null) : Outcome.Failure(null);
 	}
 
@@ -258,7 +252,7 @@ class Turtle {
 	}
 
 	public static function getItemDetail(slot:TurtleSlot, ?detailed:Bool = false):Option<ItemInspect> {
-		var r = cc.Turtle.getItemDetail(slot + 1); // FIXME: can take detailed as flag. Has to be fixed upstream
+		var r = cc.Turtle.getItemDetail(slot.toCCSlot()); // FIXME: can take detailed as flag. Has to be fixed upstream
 
 		if (r == null) {
 			return None;
diff --git a/src/kernel/turtle/TurtleSlot.hx b/src/kernel/turtle/TurtleSlot.hx
new file mode 100644
index 0000000..9ca72cf
--- /dev/null
+++ b/src/kernel/turtle/TurtleSlot.hx
@@ -0,0 +1,26 @@
+package kernel.turtle;
+
+using tink.CoreApi;
+
+/**
+	The slot nummber for turtle inventory. 0 based. Assured to be in range.
+**/
+abstract TurtleSlot(Int) to Int {
+	public function new(i:Int) {
+		if (i >= 0 && i < Turtle.MAX_SLOTS) {
+			this = i;
+		} else {
+			throw new Error("Slot not in range: " + i);
+		}
+	}
+
+	@:from
+	public static function fromInt(i:Int) {
+		return new TurtleSlot(i);
+	}
+
+	@:allow(kernel.turtle)
+	private inline function toCCSlot():Int {
+		return this + 1;
+	}
+}
diff --git a/src/kernel/turtle/Types.hx b/src/kernel/turtle/Types.hx
index 6029b2d..0d80521 100644
--- a/src/kernel/turtle/Types.hx
+++ b/src/kernel/turtle/Types.hx
@@ -22,8 +22,3 @@ typedef ItemInspect = {
 	public var damage:Int;
 	public var count:Int;
 }
-
-/**
-	The slot nummber for turtle inventory. 0 based.
-**/
-typedef TurtleSlot = Int;
diff --git a/src/lib/turtle/InvManager.hx b/src/lib/turtle/InvManager.hx
index be10abd..f89bd88 100644
--- a/src/lib/turtle/InvManager.hx
+++ b/src/lib/turtle/InvManager.hx
@@ -1,10 +1,8 @@
 package lib.turtle;
 
 import kernel.turtle.Types.ToolSide;
-import lua.Result;
-import kernel.peripherals.Side;
 import kernel.log.Log;
-import kernel.turtle.Types.TurtleSlot;
+import kernel.turtle.TurtleSlot;
 import kernel.turtle.Types.InteractDirections;
 import kernel.turtle.Turtle;