diff --git a/src/evalfunc.c b/src/evalfunc.c
index 340ecf0..4f0bb5c 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -4944,7 +4944,7 @@
 	    item = list_find(l, (long)tv_get_number_chk(&argvars[2], &error));
 	    idx = l->lv_u.mat.lv_idx;
 	    if (argvars[3].v_type != VAR_UNKNOWN)
-		ic = (int)tv_get_number_chk(&argvars[3], &error);
+		ic = (int)tv_get_bool_chk(&argvars[3], &error);
 	    if (error)
 		item = NULL;
 	}
diff --git a/src/testdir/test_vim9_func.vim b/src/testdir/test_vim9_func.vim
index 11a6ddd..04f8d7a 100644
--- a/src/testdir/test_vim9_func.vim
+++ b/src/testdir/test_vim9_func.vim
@@ -1497,6 +1497,10 @@
   assert_equal(0, count('ABC ABC ABC', 'b', false))
 enddef
 
+def Test_index()
+  assert_equal(3, index(['a', 'b', 'a', 'B'], 'b', 2, true))
+enddef
+
 def Test_expand()
   split SomeFile
   assert_equal(['SomeFile'], expand('%', true, true))
diff --git a/src/version.c b/src/version.c
index 2bf4914..388be57 100644
--- a/src/version.c
+++ b/src/version.c
@@ -755,6 +755,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1576,
+/**/
     1575,
 /**/
     1574,