diff --git a/src/testdir/test_json.vim b/src/testdir/test_json.vim
index ecca038..bd348fc 100644
--- a/src/testdir/test_json.vim
+++ b/src/testdir/test_json.vim
@@ -145,6 +145,8 @@
   call assert_equal("", json_decode('""'))
 
   call assert_equal({'n': 1}, json_decode('{"n":1,}'))
+  call assert_fails("call json_decode(\"{'n':'1',}\")", 'E474:')
+  call assert_fails("call json_decode(\"'n'\")", 'E474:')
 
   call assert_fails('call json_decode("\"")', "E474:")
   call assert_fails('call json_decode("blah")', "E474:")
@@ -255,8 +257,11 @@
   call assert_equal(v:none, js_decode(''))
   call assert_equal(type(v:none), type(js_decode('')))
   call assert_equal("", js_decode('""'))
+  call assert_equal("", js_decode("''"))
 
+  call assert_equal('n', js_decode("'n'"))
   call assert_equal({'n': 1}, js_decode('{"n":1,}'))
+  call assert_equal({'n': '1'}, js_decode("{'n':'1',}"))
 
   call assert_fails('call js_decode("\"")', "E474:")
   call assert_fails('call js_decode("blah")', "E474:")