diff --git AC-Vector.cabal AC-Vector.cabal
index ddb9e39..5081d1b 100644
--- AC-Vector.cabal
+++ AC-Vector.cabal
@@ -1,6 +1,6 @@
 Cabal-Version: >= 1.6
 Name:          AC-Vector
-Version:       2.3.2
+Version:       2.4.0
 x-revision: 1
 Stability:     Experimental
 Synopsis:      Efficient geometric vectors and transformations.
@@ -44,5 +44,5 @@ Library
     Data.BoundingBox.B2,
     Data.BoundingBox.B3,
     Data.BoundingBox.B4
-  Build-Depends:   base >= 4 && < 5
+  Build-Depends:   base >= 4.9 && < 5
   HS-Source-Dirs:  .
diff --git Data/Vector/Transform/T1.hs Data/Vector/Transform/T1.hs
index bc892a8..9c66b33 100644
--- Data/Vector/Transform/T1.hs
+++ Data/Vector/Transform/T1.hs
@@ -4,6 +4,7 @@
 
 module Data.Vector.Transform.T1 where
 
+import Data.Semigroup
 import Data.Monoid
 
 import Data.Vector.Class
@@ -23,7 +24,9 @@ data Transform1 =
 
 instance Monoid Transform1 where
   mempty = Transform1  1 0
-  mappend a b =
+
+instance Semigroup Transform1 where
+  a <> b =
     Transform1
     {
       t1_XX = t1_XX a * t1_XX b,
diff --git Data/Vector/Transform/T2.hs Data/Vector/Transform/T2.hs
index 1011935..5fce79a 100644
--- Data/Vector/Transform/T2.hs
+++ Data/Vector/Transform/T2.hs
@@ -4,6 +4,7 @@
 
 module Data.Vector.Transform.T2 where
 
+import Data.Semigroup
 import Data.Monoid
 
 import Data.Vector.Class
@@ -24,7 +25,9 @@ data Transform2 =
 
 instance Monoid Transform2 where
   mempty = Transform2  1 0 0  0 1 0
-  mappend a b =
+
+instance Semigroup Transform2 where
+  a <> b =
     Transform2
     {
       t2_XX = t2_XX a * t2_XX b  +  t2_XY a * t2_YX b,
diff --git Data/Vector/Transform/T3.hs Data/Vector/Transform/T3.hs
index 486eadf..2bed2ed 100644
--- Data/Vector/Transform/T3.hs
+++ Data/Vector/Transform/T3.hs
@@ -4,6 +4,7 @@
 
 module Data.Vector.Transform.T3 where
 
+import Data.Semigroup
 import Data.Monoid
 
 import Data.Vector.Class
@@ -25,7 +26,9 @@ data Transform3 =
 
 instance Monoid Transform3 where
   mempty = Transform3  1 0 0 0  0 1 0 0  0 0 1 0
-  mappend a b =
+
+instance Semigroup Transform3 where
+  a <> b =
     Transform3
     {
       t3_XX = t3_XX a * t3_XX b  +  t3_XY a * t3_YX b  +  t3_XZ a * t3_ZX b,
diff --git Data/Vector/Transform/T4.hs Data/Vector/Transform/T4.hs
index ec57a08..c68b4da 100644
--- Data/Vector/Transform/T4.hs
+++ Data/Vector/Transform/T4.hs
@@ -4,6 +4,7 @@
 
 module Data.Vector.Transform.T4 where
 
+import Data.Semigroup
 import Data.Monoid
 
 import Data.Vector.Class
@@ -26,7 +27,9 @@ data Transform4 =
 
 instance Monoid Transform4 where
   mempty = Transform4  1 0 0 0 0  0 1 0 0 0  0 0 1 0 0  0 0 0 1 0
-  mappend a b =
+
+instance Semigroup Transform4 where
+  a <> b =
     Transform4
     {
       t4_XX = t4_XX a * t4_XX b  +  t4_XY a * t4_YX b  +  t4_XZ a * t4_ZX b  +  t4_XW a * t4_WX b,