diff --git a/CHANGELOG b/CHANGELOG
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,3 +1,9 @@
+New in version 2.3.6:
+- Minimum base of 4.13.
+- Locked down non-colour imports.
+- Made semigroup instances canonical.
+- Updated dependencies (for testing).
+
 New in version 2.3.5:
 - Support for MonadFail Proposal.
 - Documentation updates.
diff --git a/Data/Colour.hs b/Data/Colour.hs
--- a/Data/Colour.hs
+++ b/Data/Colour.hs
@@ -125,7 +125,7 @@
  )
 where
 
-import Data.Char
+import Data.Char (isAlphaNum, isSpace)
 import Data.Colour.Internal
 import qualified Data.Colour.SRGB.Linear
 import Data.Colour.CIE.Chromaticity (app_prec, infix_prec)
diff --git a/Data/Colour/CIE.hs b/Data/Colour/CIE.hs
--- a/Data/Colour/CIE.hs
+++ b/Data/Colour/CIE.hs
@@ -37,7 +37,7 @@
  )
 where
 
-import Data.List
+import Data.List (foldl1')
 import Data.Colour
 import Data.Colour.RGB
 import Data.Colour.SRGB.Linear
diff --git a/Data/Colour/Internal.hs b/Data/Colour/Internal.hs
--- a/Data/Colour/Internal.hs
+++ b/Data/Colour/Internal.hs
@@ -22,11 +22,9 @@
 -}
 module Data.Colour.Internal where
 
-import Data.List
+import Data.List (foldl1')
 import qualified Data.Colour.Chan as Chan
 import Data.Colour.Chan (Chan(Chan))
-import Data.Monoid
-import Data.Semigroup
 
 data Red = Red
 data Green = Green
@@ -55,12 +53,11 @@
 black = RGB Chan.empty Chan.empty Chan.empty
 
 instance (Num a) => Semigroup (Colour a) where
-  (<>) = mappend
+  (RGB r1 g1 b1) <> (RGB r2 g2 b2) =
+    RGB (r1 `Chan.add` r2) (g1 `Chan.add` g2) (b1 `Chan.add` b2)
 
 instance (Num a) => Monoid (Colour a) where
   mempty = black
-  (RGB r1 g1 b1) `mappend` (RGB r2 g2 b2) =
-    RGB (r1 `Chan.add` r2) (g1 `Chan.add` g2) (b1 `Chan.add` b2)
   mconcat l = RGB (Chan.sum lr) (Chan.sum lg) (Chan.sum lb)
    where
     (lr,lg,lb) = unzip3 (map toRGB l)
@@ -173,11 +170,10 @@
 
 -- | 'AlphaColour' forms a monoid with 'over' and 'transparent'.
 instance (Num a) => Semigroup (AlphaColour a) where
-  (<>) = mappend
+  (<>) = over
 
 instance (Num a) => Monoid (AlphaColour a) where
   mempty = transparent
-  mappend = over
 
 -- | @c1 \`atop\` c2@ returns the 'AlphaColour' produced by covering
 -- the portion of @c2@ visible by @c1@.
diff --git a/Data/Colour/Matrix.hs b/Data/Colour/Matrix.hs
--- a/Data/Colour/Matrix.hs
+++ b/Data/Colour/Matrix.hs
@@ -22,7 +22,7 @@
 -}
 module Data.Colour.Matrix where
 
-import Data.List
+import Data.List (transpose)
 
 default (Rational)
 
diff --git a/Data/Colour/RGB.hs b/Data/Colour/RGB.hs
--- a/Data/Colour/RGB.hs
+++ b/Data/Colour/RGB.hs
@@ -22,10 +22,9 @@
 -}
 module Data.Colour.RGB where
 
-import Data.List
+import Data.List (elemIndex, transpose)
 import Data.Colour.Matrix
 import Data.Colour.CIE.Chromaticity
-import Control.Applicative
 
 -- |An RGB triple for an unspecified colour space.
 data RGB a = RGB {channelRed :: !a
diff --git a/Data/Colour/RGBSpace.hs b/Data/Colour/RGBSpace.hs
--- a/Data/Colour/RGBSpace.hs
+++ b/Data/Colour/RGBSpace.hs
@@ -46,8 +46,6 @@
  )
 where
 
-import Data.Monoid
-import Data.Semigroup
 import Data.Colour.CIE.Chromaticity
 import Data.Colour.Matrix
 import Data.Colour.RGB
@@ -111,12 +109,11 @@
   TransferFunction rev for (recip g)
 
 instance (Num a) => Semigroup (TransferFunction a) where
-  (<>) = mappend
+ (TransferFunction f0 f1 f) <> (TransferFunction g0 g1 g) =
+   (TransferFunction (f0 . g0) (g1 . f1) (f*g))
 
 instance (Num a) => Monoid (TransferFunction a) where
  mempty = linearTransferFunction
- (TransferFunction f0 f1 f) `mappend` (TransferFunction g0 g1 g) =
-   (TransferFunction (f0 . g0) (g1 . f1) (f*g))
 
 -- |An 'RGBSpace' is a colour coordinate system for colours laying
 -- 'inGamut' of 'gamut'.
diff --git a/Data/Colour/SRGB.hs b/Data/Colour/SRGB.hs
--- a/Data/Colour/SRGB.hs
+++ b/Data/Colour/SRGB.hs
@@ -33,8 +33,8 @@
  )
 where
 
-import Data.Word
-import Numeric
+import Data.Word (Word8)
+import Numeric (readHex, showHex)
 import Data.Colour.Internal (quantize)
 import Data.Colour.SRGB.Linear
 import Data.Colour.RGBSpace hiding (transferFunction)
diff --git a/Tests.hs b/Tests.hs
--- a/Tests.hs
+++ b/Tests.hs
@@ -23,13 +23,13 @@
 -}
 module Main where
 
-import System.Random
-import Data.Word
-import Control.Monad
-import Test.QuickCheck
+import Data.Word (Word8)
+import Control.Monad (liftM, liftM2, liftM3)
+import Test.QuickCheck ( Arbitrary, CoArbitrary, Gen, Property
+                       , (==>), arbitrary, choose, coarbitrary, forAll
+                       )
 import Test.Framework (defaultMain, defaultMainWithOpts, testGroup)
 import Test.Framework.Providers.QuickCheck2 (testProperty)
-import Data.Monoid
 
 import Data.Colour.Matrix
 import Data.Colour
diff --git a/colour.cabal b/colour.cabal
--- a/colour.cabal
+++ b/colour.cabal
@@ -1,5 +1,5 @@
 Name:                colour
-Version:             2.3.5
+Version:             2.3.6
 Cabal-Version:       >= 1.10
 License:             MIT
 License-file:        LICENSE
@@ -13,12 +13,12 @@
                      Colours can be blended and composed.
                      Various colour spaces are supported.
                      A module of colour names ("Data.Colour.Names") is provided.
-Tested-with:         GHC == 8.6.4
+Tested-with:         GHC == 8.8.4
 data-files:          README CHANGELOG
 
 Library
   default-language:  Haskell98
-  Build-Depends:     base >= 4.9 && < 5
+  Build-Depends:     base >= 4.13 && < 5
   Exposed-Modules:   Data.Colour
                      Data.Colour.SRGB
                      Data.Colour.SRGB.Linear
@@ -34,12 +34,26 @@
                      Data.Colour.Matrix
                      Data.Colour.CIE.Chromaticity
 test-suite test-colour
-    default-language:  Haskell98
-    type:       exitcode-stdio-1.0
-    main-is:    Tests.hs
-    build-depends: base >= 4.9 && < 5,
-                   QuickCheck >= 2.5 && < 2.14,
-                   random >= 1.0 && < 1.2,
-                   test-framework >= 0.8 && < 0.9,
-                   test-framework-quickcheck2 >= 0.3 && < 0.4
-
+  default-language:  Haskell98
+  type:              exitcode-stdio-1.0
+  main-is:           Tests.hs
+  build-depends: base >= 4.13 && < 5,
+                 colour,
+                 QuickCheck >= 2.5 && < 2.15,
+                 random >= 1.0 && < 1.2,
+                 test-framework >= 0.8 && < 0.9,
+                 test-framework-quickcheck2 >= 0.3 && < 0.4
+  Other-Modules:   Data.Colour
+                   Data.Colour.SRGB
+                   Data.Colour.SRGB.Linear
+                   Data.Colour.CIE
+                   Data.Colour.CIE.Illuminant
+                   Data.Colour.RGBSpace
+                   Data.Colour.RGBSpace.HSL
+                   Data.Colour.RGBSpace.HSV
+                   Data.Colour.Names
+                   Data.Colour.Internal
+                   Data.Colour.Chan
+                   Data.Colour.RGB
+                   Data.Colour.Matrix
+                   Data.Colour.CIE.Chromaticity