diff --git a/slides/gen_index.sh b/slides/gen_index.sh
index 8a59c9c2b14473b84606be18cac16d9591ae9d65..35392f46f19fb7c7672096c2618751ef90f8fa33 100755
--- a/slides/gen_index.sh
+++ b/slides/gen_index.sh
@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/bin/bash
 
 OIFS=$IFS
 NUM_LINE=2