diff --git a/CHANGELOG.markdown b/CHANGELOG.markdown
--- a/CHANGELOG.markdown
+++ b/CHANGELOG.markdown
@@ -1,3 +1,8 @@
+1.20.1
+------
+* Fixed doctests broken by the previous change.
+* Unboxed vector instances for various linear data types now use unpacked integers even on older GHCs.
+
 1.20
 ----
 * `inv22`, `inv33` and `inv44` no longer attempt an epsilon check. They no longer return a `Maybe` result as a consequence.
diff --git a/linear.cabal b/linear.cabal
--- a/linear.cabal
+++ b/linear.cabal
@@ -1,6 +1,6 @@
 name:          linear
 category:      Math, Algebra
-version:       1.20
+version:       1.20.1
 license:       BSD3
 cabal-version: >= 1.8
 license-file:  LICENSE
diff --git a/src/Linear/Matrix.hs b/src/Linear/Matrix.hs
--- a/src/Linear/Matrix.hs
+++ b/src/Linear/Matrix.hs
@@ -43,7 +43,6 @@
 import Data.Distributive
 import Data.Foldable as Foldable
 import Data.Functor.Rep
-import Linear.Epsilon
 import Linear.Quaternion
 import Linear.V2
 import Linear.V3
@@ -337,8 +336,8 @@
 -- |2x2 matrix inverse.
 --
 -- >>> inv22 $ V2 (V2 1 2) (V2 3 4)
--- Just (V2 (V2 (-2.0) 1.0) (V2 1.5 (-0.5)))
-inv22 :: (Epsilon a, Floating a) => M22 a -> M22 a
+-- V2 (V2 (-2.0) 1.0) (V2 1.5 (-0.5))
+inv22 :: Floating a => M22 a -> M22 a
 inv22 m@(V2 (V2 a b) (V2 c d)) = (1 / det) *!! V2 (V2 d (-b)) (V2 (-c) a)
   where det = det22 m
 {-# INLINE inv22 #-}
@@ -346,8 +345,8 @@
 -- |3x3 matrix inverse.
 --
 -- >>> inv33 $ V3 (V3 1 2 4) (V3 4 2 2) (V3 1 1 1)
--- Just (V3 (V3 0.0 0.5 (-1.0)) (V3 (-0.5) (-0.75) 3.5) (V3 0.5 0.25 (-1.5)))
-inv33 :: (Epsilon a, Floating a) => M33 a -> M33 a
+-- V3 (V3 0.0 0.5 (-1.0)) (V3 (-0.5) (-0.75) 3.5) (V3 0.5 0.25 (-1.5))
+inv33 :: Floating a => M33 a -> M33 a
 inv33 m@(V3 (V3 a b c)
             (V3 d e f)
             (V3 g h i))
@@ -377,7 +376,7 @@
 {-# INLINE transpose #-}
 
 -- |4x4 matrix inverse.
-inv44 :: (Epsilon a, Fractional a) => M44 a -> M44 a
+inv44 :: Fractional a => M44 a -> M44 a
 inv44 (V4 (V4 i00 i01 i02 i03)
           (V4 i10 i11 i12 i13)
           (V4 i20 i21 i22 i23)
diff --git a/src/Linear/V0.hs b/src/Linear/V0.hs
--- a/src/Linear/V0.hs
+++ b/src/Linear/V0.hs
@@ -269,6 +269,12 @@
 instance U.Unbox (V0 a)
 
 instance M.MVector U.MVector (V0 a) where
+  {-# INLINE basicLength #-}
+  {-# INLINE basicUnsafeSlice #-}
+  {-# INLINE basicOverlaps #-}
+  {-# INLINE basicUnsafeNew #-}
+  {-# INLINE basicUnsafeRead #-}
+  {-# INLINE basicUnsafeWrite #-}
   basicLength (MV_V0 n) = n
   basicUnsafeSlice _ n _ = MV_V0 n
   basicOverlaps _ _ = False
@@ -277,9 +283,15 @@
   basicUnsafeWrite _ _ _ = return ()
 #if MIN_VERSION_vector(0,11,0)
   basicInitialize _ = return ()
+  {-# INLINE basicInitialize #-}
 #endif
 
 instance G.Vector U.Vector (V0 a) where
+  {-# INLINE basicUnsafeFreeze #-}
+  {-# INLINE basicUnsafeThaw   #-}
+  {-# INLINE basicLength       #-}
+  {-# INLINE basicUnsafeSlice  #-}
+  {-# INLINE basicUnsafeIndexM #-}
   basicUnsafeFreeze (MV_V0 n) = return (V_V0 n)
   basicUnsafeThaw (V_V0 n) = return (MV_V0 n)
   basicLength (V_V0 n) = n
diff --git a/src/Linear/V1.hs b/src/Linear/V1.hs
--- a/src/Linear/V1.hs
+++ b/src/Linear/V1.hs
@@ -289,6 +289,12 @@
 instance U.Unbox a => U.Unbox (V1 a)
 
 instance U.Unbox a => M.MVector U.MVector (V1 a) where
+  {-# INLINE basicLength #-}
+  {-# INLINE basicUnsafeSlice #-}
+  {-# INLINE basicOverlaps #-}
+  {-# INLINE basicUnsafeNew #-}
+  {-# INLINE basicUnsafeRead #-}
+  {-# INLINE basicUnsafeWrite #-}
   basicLength (MV_V1 v) = M.basicLength v
   basicUnsafeSlice m n (MV_V1 v) = MV_V1 (M.basicUnsafeSlice m n v)
   basicOverlaps (MV_V1 v) (MV_V1 u) = M.basicOverlaps v u
@@ -297,9 +303,15 @@
   basicUnsafeWrite (MV_V1 v) i (V1 x) = M.basicUnsafeWrite v i x
 #if MIN_VERSION_vector(0,11,0)
   basicInitialize (MV_V1 v) = M.basicInitialize v
+  {-# INLINE basicInitialize #-}
 #endif
 
 instance U.Unbox a => G.Vector U.Vector (V1 a) where
+  {-# INLINE basicUnsafeFreeze #-}
+  {-# INLINE basicUnsafeThaw   #-}
+  {-# INLINE basicLength       #-}
+  {-# INLINE basicUnsafeSlice  #-}
+  {-# INLINE basicUnsafeIndexM #-}
   basicUnsafeFreeze (MV_V1 v) = liftM V_V1 (G.basicUnsafeFreeze v)
   basicUnsafeThaw (V_V1 v) = liftM MV_V1 (G.basicUnsafeThaw v)
   basicLength (V_V1 v) = G.basicLength v
diff --git a/src/Linear/V2.hs b/src/Linear/V2.hs
--- a/src/Linear/V2.hs
+++ b/src/Linear/V2.hs
@@ -330,11 +330,17 @@
   each = traverse
   {-# INLINE each #-}
 
-data instance U.Vector    (V2 a) =  V_V2 !Int (U.Vector    a)
-data instance U.MVector s (V2 a) = MV_V2 !Int (U.MVector s a)
+data instance U.Vector    (V2 a) =  V_V2 {-# UNPACK #-} !Int !(U.Vector    a)
+data instance U.MVector s (V2 a) = MV_V2 {-# UNPACK #-} !Int !(U.MVector s a)
 instance U.Unbox a => U.Unbox (V2 a)
 
 instance U.Unbox a => M.MVector U.MVector (V2 a) where
+  {-# INLINE basicLength #-}
+  {-# INLINE basicUnsafeSlice #-}
+  {-# INLINE basicOverlaps #-}
+  {-# INLINE basicUnsafeNew #-}
+  {-# INLINE basicUnsafeRead #-}
+  {-# INLINE basicUnsafeWrite #-}
   basicLength (MV_V2 n _) = n
   basicUnsafeSlice m n (MV_V2 _ v) = MV_V2 n (M.basicUnsafeSlice (2*m) (2*n) v)
   basicOverlaps (MV_V2 _ v) (MV_V2 _ u) = M.basicOverlaps v u
@@ -350,9 +356,15 @@
        M.basicUnsafeWrite v (o+1) y
 #if MIN_VERSION_vector(0,11,0)
   basicInitialize (MV_V2 _ v) = M.basicInitialize v
+  {-# INLINE basicInitialize #-}
 #endif
 
 instance U.Unbox a => G.Vector U.Vector (V2 a) where
+  {-# INLINE basicUnsafeFreeze #-}
+  {-# INLINE basicUnsafeThaw   #-}
+  {-# INLINE basicLength       #-}
+  {-# INLINE basicUnsafeSlice  #-}
+  {-# INLINE basicUnsafeIndexM #-}
   basicUnsafeFreeze (MV_V2 n v) = liftM ( V_V2 n) (G.basicUnsafeFreeze v)
   basicUnsafeThaw   ( V_V2 n v) = liftM (MV_V2 n) (G.basicUnsafeThaw   v)
   basicLength       ( V_V2 n _) = n
diff --git a/src/Linear/V3.hs b/src/Linear/V3.hs
--- a/src/Linear/V3.hs
+++ b/src/Linear/V3.hs
@@ -353,11 +353,17 @@
   each = traverse
   {-# INLINE each #-}
 
-data instance U.Vector    (V3 a) =  V_V3 !Int (U.Vector    a)
-data instance U.MVector s (V3 a) = MV_V3 !Int (U.MVector s a)
+data instance U.Vector    (V3 a) =  V_V3 {-# UNPACK #-} !Int !(U.Vector    a)
+data instance U.MVector s (V3 a) = MV_V3 {-# UNPACK #-} !Int !(U.MVector s a)
 instance U.Unbox a => U.Unbox (V3 a)
 
 instance U.Unbox a => M.MVector U.MVector (V3 a) where
+  {-# INLINE basicLength #-}
+  {-# INLINE basicUnsafeSlice #-}
+  {-# INLINE basicOverlaps #-}
+  {-# INLINE basicUnsafeNew #-}
+  {-# INLINE basicUnsafeRead #-}
+  {-# INLINE basicUnsafeWrite #-}
   basicLength (MV_V3 n _) = n
   basicUnsafeSlice m n (MV_V3 _ v) = MV_V3 n (M.basicUnsafeSlice (3*m) (3*n) v)
   basicOverlaps (MV_V3 _ v) (MV_V3 _ u) = M.basicOverlaps v u
@@ -375,9 +381,15 @@
        M.basicUnsafeWrite v (o+2) z
 #if MIN_VERSION_vector(0,11,0)
   basicInitialize (MV_V3 _ v) = M.basicInitialize v
+  {-# INLINE basicInitialize #-}
 #endif
 
 instance U.Unbox a => G.Vector U.Vector (V3 a) where
+  {-# INLINE basicUnsafeFreeze #-}
+  {-# INLINE basicUnsafeThaw   #-}
+  {-# INLINE basicLength       #-}
+  {-# INLINE basicUnsafeSlice  #-}
+  {-# INLINE basicUnsafeIndexM #-}
   basicUnsafeFreeze (MV_V3 n v) = liftM ( V_V3 n) (G.basicUnsafeFreeze v)
   basicUnsafeThaw   ( V_V3 n v) = liftM (MV_V3 n) (G.basicUnsafeThaw   v)
   basicLength       ( V_V3 n _) = n
diff --git a/src/Linear/V4.hs b/src/Linear/V4.hs
--- a/src/Linear/V4.hs
+++ b/src/Linear/V4.hs
@@ -495,8 +495,8 @@
 instance Each (V4 a) (V4 b) a b where
   each = traverse
 
-data instance U.Vector    (V4 a) =  V_V4 !Int (U.Vector    a)
-data instance U.MVector s (V4 a) = MV_V4 !Int (U.MVector s a)
+data instance U.Vector    (V4 a) =  V_V4 {-# UNPACK #-} !Int !(U.Vector    a)
+data instance U.MVector s (V4 a) = MV_V4 {-# UNPACK #-} !Int !(U.MVector s a)
 instance U.Unbox a => U.Unbox (V4 a)
 
 instance U.Unbox a => M.MVector U.MVector (V4 a) where