diff --git a/src/cmd/test/main.go b/src/cmd/test/main.go
index 3055a0c..588b1ce 100644
--- a/src/cmd/test/main.go
+++ b/src/cmd/test/main.go
@@ -30,8 +30,8 @@ func main() {
 	fmt.Println(m)
 	fmt.Println(slicex.MakeMap(
 		s,
-		func(v Struct) string {
-			return v.Name
+		func(s []Struct, i int) string {
+			return s[i].Name
 		},
 	))
 
diff --git a/src/slicex/main.go b/src/slicex/main.go
index 0e4f457..369f9b6 100644
--- a/src/slicex/main.go
+++ b/src/slicex/main.go
@@ -2,14 +2,14 @@ package slicex
 
 func MakeMap[K comparable, V any](
 	values []V,
-	fn func(V) (K),
+	fn func([]V, int) (K),
 ) map[K] V {
 	var k K
 
 	r := make(map[K] V)
-	for _, v := range values {
-		k = fn(v)
-		r[k] = v
+	for i, _ := range values {
+		k = fn(values, i)
+		r[k] = values[i]
 	}
 
 	return r