diff --git a/arena/arena.go b/arena/arena.go
index 7f32a61..3bcc728 100644
--- a/arena/arena.go
+++ b/arena/arena.go
@@ -24,7 +24,7 @@ func New[T any](arena Arena) *T {
 //
 // Note: Accessing the returned slice after calling Reset is unsafe and may result in a fault.
 func MakeSlice[T any](arena Arena, len, cap int) []T {
-	ptr, err := arena(ACTION_ALLOC, mem.Sizeof[T]()*uintptr(len), mem.Alignof[T](), nil)
+	ptr, err := arena(ACTION_ALLOC, mem.Sizeof[T]()*uintptr(cap), mem.Alignof[T](), nil)
 	if err != nil {
 		panic(err)
 	}