diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,11 @@
+0.9.2
+-----
+
+* Fix code generation for query flag
+  ([#11](https://github.com/haskell-servant/servant-js/issues/11))
+* Improve error handling in vanilla backend
+  ([#9](https://github.com/haskell-servant/servant-js/pull/9))
+
 0.9.1
 -----
 
diff --git a/servant-js.cabal b/servant-js.cabal
--- a/servant-js.cabal
+++ b/servant-js.cabal
@@ -1,5 +1,5 @@
 name:                servant-js
-version:             0.9.1
+version:             0.9.2
 synopsis:            Automatically derive javascript functions to query servant webservices.
 description:
   Automatically derive javascript functions to query servant webservices.
@@ -66,11 +66,11 @@
     buildable: False
 
   build-depends:    base             >= 4.7 && < 5
-                  , aeson            >= 0.7  && < 1.1
+                  , aeson            >= 0.7  && < 1.2
                   , filepath         >= 1
                   , lens             >= 4
-                  , servant          == 0.9.*
-                  , servant-server   == 0.9.*
+                  , servant
+                  , servant-server
                   , servant-js
                   , stm
                   , transformers
diff --git a/src/Servant/JS/Internal.hs b/src/Servant/JS/Internal.hs
--- a/src/Servant/JS/Internal.hs
+++ b/src/Servant/JS/Internal.hs
@@ -183,7 +183,7 @@
            <> "=' + encodeURIComponent("
            <> name
            <> if notTheEnd then ") + '" else ")"
-    Flag   -> name <> "="
+    Flag   -> name <> "'"
     List   -> name
            <> "[]=' + encodeURIComponent("
            <> name
diff --git a/src/Servant/JS/Vanilla.hs b/src/Servant/JS/Vanilla.hs
--- a/src/Servant/JS/Vanilla.hs
+++ b/src/Servant/JS/Vanilla.hs
@@ -29,28 +29,28 @@
 -- | js codegen using XmlHttpRequest
 generateVanillaJSWith :: CommonGeneratorOptions -> AjaxReq -> Text
 generateVanillaJSWith opts req = "\n" <>
-    fname <> " = function(" <> argsStr <> ")\n"
- <> "{\n"
+    fname <> " = function(" <> argsStr <> ") {\n"
  <> "  var xhr = new XMLHttpRequest();\n"
  <> "  xhr.open('" <> decodeUtf8 method <> "', " <> url <> ", true);\n"
  <>    reqheaders
- <> "  xhr.setRequestHeader(\"Accept\",\"application/json\");\n"
- <> (if isJust (req ^. reqBody) then "  xhr.setRequestHeader(\"Content-Type\",\"application/json\");\n" else "")
- <> "  xhr.onreadystatechange = function (e) {\n"
- <> "    if (xhr.readyState == 4) {\n"
- <> "      if (xhr.status == 204 || xhr.status == 205) {\n"
- <> "        onSuccess();\n"
- <> "      } else if (xhr.status >= 200 && xhr.status < 300) {\n"
- <> "        var value = JSON.parse(xhr.responseText);\n"
- <> "        onSuccess(value);\n"
+ <> "  xhr.setRequestHeader('Accept', 'application/json');\n"
+ <> (if isJust (req ^. reqBody) then "  xhr.setRequestHeader('Content-Type', 'application/json');\n" else "")
+ <> "  xhr.onreadystatechange = function () {\n"
+ <> "    var res = null;\n"
+ <> "    if (xhr.readyState === 4) {\n"
+ <> "      if (xhr.status === 204 || xhr.status === 205) {\n"
+ <> "        " <> onSuccess <> "();\n"
+ <> "      } else if (xhr.status >= 200 && xhr.status < 300 && xhr.responseType === 'json') {\n"
+ <> "        try { res = JSON.parse(xhr.responseText); } catch (e) { " <> onError <> "(e); }\n"
+ <> "        if (res) " <> onSuccess <> "(res);\n"
  <> "      } else {\n"
- <> "        var value = JSON.parse(xhr.responseText);\n"
- <> "        onError(value);\n"
+ <> "        try { res = JSON.parse(xhr.responseText); } catch (e) { " <> onError <> "(e); }\n"
+ <> "        if (res) " <> onError <> "(res);\n"
  <> "      }\n"
  <> "    }\n"
- <> "  }\n"
+ <> "  };\n"
  <> "  xhr.send(" <> dataBody <> ");\n"
- <> "}\n"
+ <> "};\n"
 
   where argsStr = T.intercalate ", " args
         args = captures
@@ -79,7 +79,7 @@
 
         dataBody =
           if isJust (req ^. reqBody)
-            then "JSON.stringify(body)\n"
+            then "JSON.stringify(body)"
             else "null"
 
 
diff --git a/test/Servant/JSSpec.hs b/test/Servant/JSSpec.hs
--- a/test/Servant/JSSpec.hs
+++ b/test/Servant/JSSpec.hs
@@ -26,6 +26,7 @@
 
 import           Servant.API.Internal.Test.ComprehensiveAPI
 import           Servant.API.ContentTypes
+import           Servant.API.QueryParam
 import           Servant.JS
 import           Servant.JS.Internal
 import qualified Servant.JS.Angular           as NG
@@ -42,6 +43,7 @@
 -- * specs
 
 type TestAPI = "simple" :> ReqBody '[JSON,FormUrlEncoded] Text :> Post '[JSON] Bool
+          :<|> "params" :> QueryParam "foo" Text :> QueryFlag "flag" :> Get '[JSON] Bool
           :<|> "has.extension" :> Get '[FormUrlEncoded,JSON] Bool
 
 type TopLevelRawAPI = "something" :> Get '[JSON] Int