diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,5 +1,9 @@
 # Changelog for http-client
 
+## 0.6.1.1
+
+* Ensure that `Int` parsing doesn't overflow [#383](https://github.com/snoyberg/http-client/issues/383)
+
 ## 0.6.1
 
 * Add `setUriEither` to `Network.HTTP.Client.Internal`
diff --git a/Network/HTTP/Client.hs b/Network/HTTP/Client.hs
--- a/Network/HTTP/Client.hs
+++ b/Network/HTTP/Client.hs
@@ -40,7 +40,7 @@
 -- application which will make a large number of requests to different hosts,
 -- and will never make more than one connection to a single host, then sharing
 -- a 'Manager' will result in idle connections being kept open longer than
--- necessary. In such a situation, it makes sense to use 'withManager' around
+-- necessary. In such a situation, it makes sense to use 'newManager' before
 -- each new request, to avoid running out of file descriptors. (Note that the
 -- 'managerIdleConnectionCount' setting mitigates the risk of leaking too many
 -- file descriptors.)
diff --git a/Network/HTTP/Client/Request.hs b/Network/HTTP/Client/Request.hs
--- a/Network/HTTP/Client/Request.hs
+++ b/Network/HTTP/Client/Request.hs
@@ -263,7 +263,7 @@
             ':':rest -> maybe
                 (Left "Invalid port")
                 return
-                (readDec rest)
+                (readPositiveInt rest)
             -- Otherwise, use the default port
             _ -> case sec of
                     False {- HTTP -} -> return 80
diff --git a/Network/HTTP/Client/Response.hs b/Network/HTTP/Client/Response.hs
--- a/Network/HTTP/Client/Response.hs
+++ b/Network/HTTP/Client/Response.hs
@@ -87,7 +87,7 @@
 getResponse timeout' req@(Request {..}) mconn cont = do
     let conn = managedResource mconn
     StatusHeaders s version hs <- parseStatusHeaders conn timeout' cont
-    let mcl = lookup "content-length" hs >>= readDec . S8.unpack
+    let mcl = lookup "content-length" hs >>= readPositiveInt . S8.unpack
         isChunked = ("transfer-encoding", CI.mk "chunked") `elem` map (second CI.mk) hs
 
         -- should we put this connection back into the connection manager?
diff --git a/Network/HTTP/Client/Util.hs b/Network/HTTP/Client/Util.hs
--- a/Network/HTTP/Client/Util.hs
+++ b/Network/HTTP/Client/Util.hs
@@ -1,15 +1,15 @@
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 module Network.HTTP.Client.Util
-    ( readDec
+    ( readPositiveInt
     ) where
 
-import qualified Data.Text as T
-import qualified Data.Text.Read
+import Text.Read (readMaybe)
+import Control.Monad (guard)
 
-readDec :: Integral i => String -> Maybe i
-readDec s =
-    case Data.Text.Read.decimal $ T.pack s of
-        Right (i, t)
-            | T.null t -> Just i
-        _ -> Nothing
+-- | Read a positive 'Int', accounting for overflow
+readPositiveInt :: String -> Maybe Int
+readPositiveInt s = do
+  i <- readMaybe s
+  guard $ i >= 0
+  Just i
diff --git a/http-client.cabal b/http-client.cabal
--- a/http-client.cabal
+++ b/http-client.cabal
@@ -1,5 +1,5 @@
 name:                http-client
-version:             0.6.1
+version:             0.6.1.1
 synopsis:            An HTTP client engine
 description:         Hackage documentation generation is not reliable. For up to date documentation, please see: <http://www.stackage.org/package/http-client>.
 homepage:            https://github.com/snoyberg/http-client
diff --git a/test-nonet/Network/HTTP/ClientSpec.hs b/test-nonet/Network/HTTP/ClientSpec.hs
--- a/test-nonet/Network/HTTP/ClientSpec.hs
+++ b/test-nonet/Network/HTTP/ClientSpec.hs
@@ -254,3 +254,8 @@
         ok <- readIORef okRef
         unless ok $
           throwIO (ErrorCall "already closed")
+
+    it "does not allow port overflow #383" $ do
+      case parseRequest "https://o_O:18446744072699450606" of
+        Left _ -> pure () :: IO ()
+        Right req -> error $ "Invalid request: " ++ show req