diff --git a/3.insertionSort.md b/3.insertionSort.md
index c828cb3..56d6fab 100644
--- a/3.insertionSort.md
+++ b/3.insertionSort.md
@@ -58,7 +58,7 @@ func insertionSort(arr []int) []int {
 		current := arr[i]
 		for preIndex >= 0 && arr[preIndex] > current {
 			arr[preIndex+1] = arr[preIndex]
-			preIndex -= 1
+			preIndex--
 		}
 		arr[preIndex+1] = current
 	}