diff --git a/runtime/doc/eval.txt b/runtime/doc/eval.txt
index 906a869..8340bf2 100644
--- a/runtime/doc/eval.txt
+++ b/runtime/doc/eval.txt
@@ -1752,6 +1752,7 @@
 argv( )				List	the argument list
 assert_equal( {exp}, {act} [, {msg}]) none  assert {exp} equals {act}
 assert_exception({error} [, {msg}])   none  assert {error} is in v:exception
+assert_fails( {cmd} [, {error}])      none  assert {cmd} fails
 assert_false( {actual} [, {msg}])     none  assert {actual} is false
 assert_true( {actual} [, {msg}])      none  assert {actual} is true
 asin( {expr})			Float	arc sine of {expr}
@@ -2207,6 +2208,11 @@
 			  call assert_exception('E492:')
 			endtry
 
+assert_fails({cmd} [, {error}])					*assert_fails()*
+		Run {cmd} and add an error message to |v:errors| if it does
+		NOT produce an error.
+		When {error} is given it must match |v:errmsg|.
+
 assert_false({actual} [, {msg}])				*assert_false()*
 		When {actual} is not false an error message is added to
 		|v:errors|, like with |assert_equal()|.