diff --git a/CHANGELOG b/CHANGELOG
index 0206702b02..07beb8f36e 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,3 +1,10 @@
+git-annex (6.20180914) UNRELEASED; urgency=medium
+
+  * S3: Fix url construction bug when the publicurl has been set to an url
+    that does not end with a slash.
+
+ -- Joey Hess <id@joeyh.name>  Fri, 14 Sep 2018 12:20:19 -0400
+
 git-annex (6.20180913) upstream; urgency=medium
 
   * When --batch is used with matching options like --in, --metadata,
diff --git a/Remote/S3.hs b/Remote/S3.hs
index e1cc1b8b3b..83016d11e1 100644
--- a/Remote/S3.hs
+++ b/Remote/S3.hs
@@ -21,6 +21,7 @@ import qualified Data.ByteString.Lazy as L
 import qualified Data.ByteString as BS
 import qualified Data.Map as M
 import qualified Data.Set as S
+import qualified System.FilePath.Posix as Posix
 import Data.Char
 import Network.Socket (HostName)
 import Network.HTTP.Conduit (Manager)
@@ -690,7 +691,7 @@ awsPublicUrl info = genericPublicUrl $
 	"https://" ++ T.unpack (bucket info) ++ ".s3.amazonaws.com/" 
 
 genericPublicUrl :: URLString -> BucketObject -> URLString
-genericPublicUrl baseurl p = baseurl ++ p
+genericPublicUrl baseurl p = baseurl Posix.</> p
 
 genCredentials :: CredPair -> IO AWS.Credentials
 genCredentials (keyid, secret) = AWS.Credentials