diff --git a/Aws/Core.hs b/Aws/Core.hs
--- a/Aws/Core.hs
+++ b/Aws/Core.hs
@@ -317,7 +317,7 @@
       , HTTP.queryString = HTTP.renderQuery False sqQuery
       , HTTP.requestHeaders = catMaybes [fmap (\d -> ("Date", fmtRfc822Time d)) sqDate
                                         , fmap (\c -> ("Content-Type", c)) contentType
-                                        , fmap (\md5 -> ("Content-MD5", Serialize.encode md5)) sqContentMd5
+                                        , fmap (\md5 -> ("Content-MD5", Base64.encode $ Serialize.encode md5)) sqContentMd5
                                         , fmap (\auth -> ("Authorization", auth)) sqAuthorization]
                               ++ sqAmzHeaders
                               ++ sqOtherHeaders
diff --git a/Aws/S3/Core.hs b/Aws/S3/Core.hs
--- a/Aws/S3/Core.hs
+++ b/Aws/S3/Core.hs
@@ -23,6 +23,7 @@
 import qualified Crypto.Hash.MD5                as MD5
 import qualified Data.ByteString                as B
 import qualified Data.ByteString.Char8          as B8
+import qualified Data.ByteString.Base64         as Base64
 import qualified Data.CaseInsensitive           as CI
 import qualified Data.Conduit                   as C
 import qualified Data.Serialize                 as Serialize
@@ -178,7 +179,7 @@
       sig = signature signatureCredentials HmacSHA1 stringToSign
       stringToSign = Blaze.toByteString . mconcat . intersperse (Blaze8.fromChar '\n') . concat  $
                        [[Blaze.copyByteString $ httpMethod s3QMethod]
-                       , [maybe mempty (Blaze.copyByteString . Serialize.encode) s3QContentMd5]
+                       , [maybe mempty (Blaze.copyByteString . Base64.encode . Serialize.encode) s3QContentMd5]
                        , [maybe mempty Blaze.copyByteString s3QContentType]
                        , [Blaze.copyByteString $ case ti of
                                                    AbsoluteTimestamp time -> fmtRfc822Time time
diff --git a/aws.cabal b/aws.cabal
--- a/aws.cabal
+++ b/aws.cabal
@@ -6,7 +6,7 @@
 -- The package version. See the Haskell package versioning policy
 -- (http://www.haskell.org/haskellwiki/Package_versioning_policy) for
 -- standards guiding when and how versions should be incremented.
-Version:             0.6.0
+Version:             0.6.1
 
 -- A short (one-line) description of the package.
 Synopsis:            Amazon Web Services (AWS) for Haskell