diff --git a/.travis.yml b/.travis.yml
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,7 +1,7 @@
 language: haskell
 before_install:
   # Uncomment whenever hackage is down.
-  - mkdir -p ~/.cabal && cp config ~/.cabal/config && cabal update
+  # - mkdir -p ~/.cabal && cp config ~/.cabal/config && cabal update
 
   # Try installing some of the build-deps with apt-get for speed.
   - ./travis-cabal-apt-install --only-dependencies --force-reinstall $mode
diff --git a/CHANGELOG.markdown b/CHANGELOG.markdown
--- a/CHANGELOG.markdown
+++ b/CHANGELOG.markdown
@@ -1,3 +1,7 @@
+3.7.2 [maintenance release]
+-----
+* Bug fix for `Magnify`. It was missing functional dependencies to determine its `k` parameter from `m` or `n`.
+
 3.7.1.2 [maintenance release]
 -------
 * Made the doctest test suite hide all but the exact versions of packages used to build this package to avoid problems with complicated user environments.
diff --git a/lens.cabal b/lens.cabal
--- a/lens.cabal
+++ b/lens.cabal
@@ -1,6 +1,6 @@
 name:          lens
 category:      Data, Lenses
-version:       3.7.1.2
+version:       3.7.2
 license:       BSD3
 cabal-version: >= 1.8
 license-file:  LICENSE
diff --git a/src/Control/Lens/Zoom.hs b/src/Control/Lens/Zoom.hs
--- a/src/Control/Lens/Zoom.hs
+++ b/src/Control/Lens/Zoom.hs
@@ -31,7 +31,7 @@
 import Control.Lens.Internal.Combinators
 import Control.Lens.Type
 import Control.Monad
-import Control.Monad.Reader.Class as Reader
+import Control.Monad.Reader as Reader
 import Control.Monad.State as State
 import Control.Monad.Trans.State.Lazy as Lazy
 import Control.Monad.Trans.State.Strict as Strict
@@ -39,7 +39,6 @@
 import Control.Monad.Trans.Writer.Strict as Strict
 import Control.Monad.Trans.RWS.Lazy as Lazy
 import Control.Monad.Trans.RWS.Strict as Strict
-import Control.Monad.Trans.Reader
 import Control.Monad.Trans.Error
 import Control.Monad.Trans.List
 import Control.Monad.Trans.Identity
@@ -48,6 +47,7 @@
 
 -- $setup
 -- >>> import Control.Lens
+-- >>> import Data.List.Lens (_tail)
 -- >>> import Control.Monad.State
 -- >>> import Data.Map as Map
 -- >>> import Debug.SimpleReflect.Expr as Expr
@@ -151,7 +151,7 @@
 -- many different monad transformers. Unlike 'zoom' this can change the environment of a deeply nested monad transformer.
 --
 -- Also, unlike 'zoom', this can be used with any valid 'Getter', but cannot be used with a 'Traversal' or 'Fold'.
-class (MonadReader b m, MonadReader a n) => Magnify m n k b a | m -> b, n -> a, m a -> n, n b -> m where
+class (MonadReader b m, MonadReader a n) => Magnify m n k b a | m -> b k, n -> a k, m a -> n, n b -> m where
   -- | Run a monadic action in a larger environment than it was defined in, using a 'Getter'.
   --
   -- This acts like 'Control.Monad.Reader.Class.local', but can in many cases change the type of the environment as well.
@@ -159,6 +159,15 @@
   -- This is commonly used to lift actions in a simpler Reader monad into a monad with a larger environment type.
   --
   -- This can be used to edit pretty much any monad transformer stack with an environment in it:
+  --
+  -- >>> (1,2) & magnify _2 (+1)
+  -- 3
+  --
+  -- >>> flip Reader.runReader (1,2) $ magnify _1 Reader.ask
+  -- 1
+  --
+  -- >>> flip Reader.runReader (1,2,[10..20]) $ magnify (_3._tail) Reader.ask
+  -- [11,12,13,14,15,16,17,18,19,20]
   --
   -- @
   -- 'magnify' ::             'Getter' s a -> (a -> r) -> s -> r