diff --git a/src/evalfunc.c b/src/evalfunc.c
index c9f4c45..0d79996 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -512,7 +512,7 @@
     {"assert_equal",	2, 3, f_assert_equal},
     {"assert_equalfile", 2, 2, f_assert_equalfile},
     {"assert_exception", 1, 2, f_assert_exception},
-    {"assert_fails",	1, 2, f_assert_fails},
+    {"assert_fails",	1, 3, f_assert_fails},
     {"assert_false",	1, 2, f_assert_false},
     {"assert_inrange",	3, 4, f_assert_inrange},
     {"assert_match",	2, 3, f_assert_match},
@@ -1507,7 +1507,7 @@
 }
 
 /*
- * "assert_fails(cmd [, error])" function
+ * "assert_fails(cmd [, error[, msg]])" function
  */
     static void
 f_assert_fails(typval_T *argvars, typval_T *rettv)