diff --git a/src/Data/RelativeValidity.hs b/src/Data/RelativeValidity.hs
--- a/src/Data/RelativeValidity.hs
+++ b/src/Data/RelativeValidity.hs
@@ -19,7 +19,5 @@
 class RelativeValidity a b where
     isValidFor :: a -> b -> Bool
 
-isInvalidFor
-    :: RelativeValidity a b
-    => a -> b -> Bool
+isInvalidFor :: RelativeValidity a b => a -> b -> Bool
 isInvalidFor a b = not $ isValidFor a b
diff --git a/src/Data/Validity.hs b/src/Data/Validity.hs
--- a/src/Data/Validity.hs
+++ b/src/Data/Validity.hs
@@ -64,7 +64,6 @@
     , Monoid(..)
     ) where
 
-
 import Data.Either (isRight)
 import Data.Fixed (Fixed(MkFixed), HasResolution)
 import Data.List (intercalate)
@@ -75,6 +74,7 @@
 #if MIN_VERSION_base(4,8,0)
 #else
 import Data.Monoid
+import Data.Ratio
 #endif
 import Data.Word (Word, Word16, Word32, Word64, Word8)
 import GHC.Generics
@@ -377,11 +377,11 @@
             (\(ix, e) ->
                  e <?!>
                  unwords
-                 [ "The element at index"
-                 , show (ix :: Integer)
-                 , "in the list"]) .
+                     [ "The element at index"
+                     , show (ix :: Integer)
+                     , "in the list"
+                     ]) .
         zip [0 ..]
-
 #if MIN_VERSION_base(4,9,0)
 -- | A nonempty list is valid if all the elements are valid.
 --
@@ -394,7 +394,6 @@
             , es <?!> "The rest of the elements of the nonempty list"
             ]
 #endif
-
 -- | A Maybe thing is valid if the thing inside is valid or it's nothing
 -- It makes sense to assume that 'Nothing' is valid.
 -- If Nothing wasn't valid, you wouldn't have used a Maybe
@@ -498,14 +497,14 @@
     isValid = isValidNatural
     validate = validateByChecking "Natural"
 #endif
--- | Valid if the contained 'Integer's are valid and the denominator is
+-- | Valid if the contained numbers are valid and the denominator is
 -- strictly positive.
-instance Validity Rational where
-    isValid (d :% n) = isValid n && isValid d && d > 0
-    validate (d :% n) =
+instance (Num a, Ord a, Validity a) => Validity (Ratio a) where
+    isValid (n :% d) = isValid n && isValid d && d > 0
+    validate (n :% d) =
         mconcat
-            [ d <?!> "The numerator"
-            , n <?!> "The denominator"
+            [ n <?!> "The numerator"
+            , d <?!> "The denominator"
             , (d > 0) <?@> "The denominator is strictly positive."
             ]
 
diff --git a/validity.cabal b/validity.cabal
--- a/validity.cabal
+++ b/validity.cabal
@@ -1,54 +1,60 @@
-name: validity
-version: 0.4.0.2
-cabal-version: >=1.10
-build-type: Simple
-license: MIT
-license-file: LICENSE
-copyright: Copyright: (c) 2016 Tom Sydney Kerckhove
-maintainer: syd.kerckhove@gmail.com
-homepage: https://github.com/NorfairKing/validity#readme
-synopsis: Validity typeclass
-description:
-    For more info, see <https://github.com/NorfairKing/validity the readme>.
-    .
-    Note: There are companion instance packages for this library:
-    .
-    * <https://hackage.haskell.org/package/validity-aeson validity-aeson>
-    .
-    * <https://hackage.haskell.org/package/validity-bytestring validity-bytestring>
-    .
-    * <https://hackage.haskell.org/package/validity-containers validity-containers>
-    .
-    * <https://hackage.haskell.org/package/validity-path validity-path>
-    .
-    * <https://hackage.haskell.org/package/validity-scientific validity-scientific>
-    .
-    * <https://hackage.haskell.org/package/validity-text validity-text>
-    .
-    * <https://hackage.haskell.org/package/validity-time validity-time>
-    .
-    * <https://hackage.haskell.org/package/validity-unordered-containers validity-unordered-containers>
-    .
-    * <https://hackage.haskell.org/package/validity-uuid validity-uuid>
-    .
-    * <https://hackage.haskell.org/package/validity-vector validity-vector>
-    .
-category: Validity
-author: Tom Sydney Kerckhove
+-- This file has been generated from package.yaml by hpack version 0.20.0.
+--
+-- see: https://github.com/sol/hpack
+--
+-- hash: 3d4c42c36ef5d4b468135318944bb8d8b697595fa09fe24c7207539b28f2d7ca
 
+name:           validity
+version:        0.4.0.3
+synopsis:       Validity typeclass
+description:    For more info, see <https://github.com/NorfairKing/validity the readme>.
+                .
+                Note: There are companion instance packages for this library:
+                .
+                * <https://hackage.haskell.org/package/validity-aeson validity-aeson>
+                .
+                * <https://hackage.haskell.org/package/validity-bytestring validity-bytestring>
+                .
+                * <https://hackage.haskell.org/package/validity-containers validity-containers>
+                .
+                * <https://hackage.haskell.org/package/validity-path validity-path>
+                .
+                * <https://hackage.haskell.org/package/validity-scientific validity-scientific>
+                .
+                * <https://hackage.haskell.org/package/validity-text validity-text>
+                .
+                * <https://hackage.haskell.org/package/validity-time validity-time>
+                .
+                * <https://hackage.haskell.org/package/validity-unordered-containers validity-unordered-containers>
+                .
+                * <https://hackage.haskell.org/package/validity-uuid validity-uuid>
+                .
+                * <https://hackage.haskell.org/package/validity-vector validity-vector>
+category:       Validity
+homepage:       https://github.com/NorfairKing/validity#readme
+bug-reports:    https://github.com/NorfairKing/validity/issues
+author:         Tom Sydney Kerckhove
+maintainer:     syd.kerckhove@gmail.com
+copyright:      Copyright: (c) 2016 Tom Sydney Kerckhove
+license:        MIT
+license-file:   LICENSE
+build-type:     Simple
+cabal-version:  >= 1.10
+
 source-repository head
-    type: git
-    location: https://github.com/NorfairKing/validity
+  type: git
+  location: https://github.com/NorfairKing/validity
 
 library
-    
-    if impl(ghc >=8.0.0)
-        ghc-options: -Wno-redundant-constraints
-    exposed-modules:
-        Data.RelativeValidity
-        Data.Validity
-    build-depends:
-        base >=4.7 && <5
-    default-language: Haskell2010
-    hs-source-dirs: src
-
+  hs-source-dirs:
+      src
+  build-depends:
+      base >=4.7 && <5
+  if impl(ghc >=8.0.0)
+    ghc-options: -Wno-redundant-constraints
+  exposed-modules:
+      Data.RelativeValidity
+      Data.Validity
+  other-modules:
+      Paths_validity
+  default-language: Haskell2010