diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,3 +1,7 @@
+## 1.1.7.3
+
+* Make Binary.lines O(n) instead of O(n^2) [#209](https://github.com/snoyberg/conduit/pull/209)
+
 ## 1.1.7.2
 
 * Fix for: Decompressing a specific amount of zlib data "eats" following data [#20](https://github.com/fpco/streaming-commons/issues/20)
diff --git a/Data/Conduit/Binary.hs b/Data/Conduit/Binary.hs
--- a/Data/Conduit/Binary.hs
+++ b/Data/Conduit/Binary.hs
@@ -345,20 +345,18 @@
 -- Since 0.3.0
 lines :: Monad m => Conduit S.ByteString m S.ByteString
 lines =
-    loop id
+    loop []
   where
-    loop front = await >>= maybe (finish front) (go front)
+    loop acc = await >>= maybe (finish acc) (go acc)
 
-    finish front =
-        let final = front S.empty
+    finish acc =
+        let final = S.concat $ reverse acc
          in unless (S.null final) (yield final)
 
-    go sofar more =
+    go acc more =
         case S.uncons second of
-            Just (_, second') -> yield (sofar first) >> go id second'
-            Nothing ->
-                let rest = sofar more
-                 in loop $ S.append rest
+            Just (_, second') -> yield (S.concat $ reverse $ first:acc) >> go [] second'
+            Nothing -> loop $ more:acc
       where
         (first, second) = S.breakByte 10 more
 
diff --git a/conduit-extra.cabal b/conduit-extra.cabal
--- a/conduit-extra.cabal
+++ b/conduit-extra.cabal
@@ -1,5 +1,5 @@
 Name:                conduit-extra
-Version:             1.1.7.2
+Version:             1.1.7.3
 Synopsis:            Batteries included conduit: adapters for common libraries.
 Description:
     The conduit package itself maintains relative small dependencies. The purpose of this package is to collect commonly used utility functions wrapping other library dependencies, without depending on heavier-weight dependencies. The basic idea is that this package should only depend on haskell-platform packages and conduit.