diff --git a/changelog b/changelog
--- a/changelog
+++ b/changelog
@@ -1,3 +1,11 @@
+2015-01-03 0.5.1
+================
+
+	* Fix the encoding of the `aud` part of the claim.
+	  Thanks to Aaron Levin for reporting and implementing the change.
+	  In addition to the fix we now also verify the shape fo the generated
+	  payload.
+
 2014-12-01 0.5.0
 ================
 
diff --git a/jwt.cabal b/jwt.cabal
--- a/jwt.cabal
+++ b/jwt.cabal
@@ -2,7 +2,7 @@
 -- documentation, see http://haskell.org/cabal/users-guide/
 
 name:                jwt
-version:             0.5.0
+version:             0.5.1
 synopsis:            JSON Web Token (JWT) decoding and encoding
 license:             MIT
 license-file:        LICENSE
@@ -75,6 +75,8 @@
                      , tasty-th >= 0.1
                      , tasty-hunit >= 0.4
                      , tasty-quickcheck >= 0.3
+                     , lens-aeson
+                     , lens
                      , HUnit
                      , QuickCheck >= 2.4.0.1
                      , cryptohash
diff --git a/src/Web/JWT.hs b/src/Web/JWT.hs
--- a/src/Web/JWT.hs
+++ b/src/Web/JWT.hs
@@ -402,7 +402,7 @@
     toJSON JWTClaimsSet{..} = object $ catMaybes [
                   fmap ("iss" .=) iss
                 , fmap ("sub" .=) sub
-                , fmap ("aud" .=) aud
+                , either ("aud" .=) ("aud" .=) <$> aud
                 , fmap ("exp" .=) exp
                 , fmap ("nbf" .=) nbf
                 , fmap ("iat" .=) iat
@@ -415,7 +415,10 @@
                      (\o -> JWTClaimsSet
                      <$> o .:? "iss"
                      <*> o .:? "sub"
-                     <*> o .:? "aud"
+                     <*> case StrictMap.lookup "aud" o of
+                         (Just as@(JSON.Array _)) -> Just <$> Right <$> parseJSON as
+                         (Just (JSON.String t))   -> pure $ Left <$> stringOrURI t
+                         _                        -> pure Nothing
                      <*> o .:? "exp"
                      <*> o .:? "nbf"
                      <*> o .:? "iat"
diff --git a/tests/src/TestRunner.hs b/tests/src/TestRunner.hs
--- a/tests/src/TestRunner.hs
+++ b/tests/src/TestRunner.hs
@@ -1,6 +1,7 @@
 module Main where
 
 import qualified Web.JWTTests
+import qualified Web.JWTInteropTests
 import qualified Web.Base64Tests
 import           Test.Tasty
 
@@ -10,6 +11,7 @@
 tests :: TestTree
 tests = testGroup "JWT Tests" [
                     Web.JWTTests.defaultTestGroup
+                  , Web.JWTInteropTests.defaultTestGroup
                   , Web.Base64Tests.defaultTestGroup
                 ]
 
diff --git a/tests/src/Web/JWTTests.hs b/tests/src/Web/JWTTests.hs
--- a/tests/src/Web/JWTTests.hs
+++ b/tests/src/Web/JWTTests.hs
@@ -143,6 +143,27 @@
         jwt = decodeAndVerifySignature secret' $ encodeSigned HS256 secret' cs
     Just cs @=? fmap claims jwt
 
+case_encodeDecodeJWTClaimsSetWithSingleAud = do
+    let now = 1234
+        cs = def {
+            iss = stringOrURI "Foo"
+          , aud = Left <$> stringOrURI "single-audience"
+          , iat = intDate now
+        }
+    let secret' = secret "secret"
+        jwt = decodeAndVerifySignature secret' $ encodeSigned HS256 secret' cs
+    Just cs @=? fmap claims jwt
+
+case_encodeDecodeJWTClaimsSetWithMultipleAud = do
+    let now = 1234
+        cs = def {
+            iss = stringOrURI "Foo"
+          , aud = Right <$> (:[]) <$> stringOrURI "audience"
+          , iat = intDate now
+        }
+    let secret' = secret "secret"
+        jwt = decodeAndVerifySignature secret' $ encodeSigned HS256 secret' cs
+    Just cs @=? fmap claims jwt
 
 prop_stringOrURIProp = f
     where f :: StringOrURI -> Bool