diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,9 @@
 # phash
 
+## 0.1.3.1
+
+  * Add `include/hs_phash.h` header
+
 ## 0.1.3.0
 
   * CLI tool now supports several more image formats
diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -6,9 +6,11 @@
 [![Hackage](https://img.shields.io/hackage/v/perceptual-hash.svg)](http://hackage.haskell.org/package/perceptual-hash)
 [![Dependencies of latest version on Hackage](https://img.shields.io/hackage-deps/v/perceptual-hash.svg)](https://hackage.haskell.org/package/perceptual-hash)
 
-This is a command-line tool to detect (potential) duplicate images. It also
-contains a Haskell [library](http://hackage.haskell.org/package/perceptual-hash).
+This is a Haskell [library](http://hackage.haskell.org/package/perceptual-hash)
+to detect (potential) duplicate images.
 
+It also contains a command-line tool.
+
 ## Use
 
 Use it on one or more directories:
@@ -41,3 +43,55 @@
 ```
 cabal install perceptual-hash -w ghc-8.6.5
 ```
+
+## Library
+
+You can find library documentation on
+[Hackage](https://hackage.haskell.org/package/perceptual-hash).
+
+### Performance
+
+This library is more performant than the pHash library for PNG
+images.
+
+```
+benchmarking fileHash/cat.png
+time                 21.42 ms   (21.20 ms .. 21.63 ms)
+                     1.000 R²   (0.999 R² .. 1.000 R²)
+mean                 21.34 ms   (21.28 ms .. 21.44 ms)
+std dev              184.3 μs   (93.40 μs .. 266.3 μs)
+
+benchmarking fileHash/frog.jpeg
+time                 18.16 ms   (18.07 ms .. 18.24 ms)
+                     1.000 R²   (1.000 R² .. 1.000 R²)
+mean                 18.24 ms   (18.12 ms .. 18.31 ms)
+std dev              230.1 μs   (161.3 μs .. 360.2 μs)
+
+benchmarking fileHash/frog.png
+time                 12.39 ms   (12.35 ms .. 12.46 ms)
+                     1.000 R²   (0.999 R² .. 1.000 R²)
+mean                 12.38 ms   (12.34 ms .. 12.43 ms)
+std dev              114.0 μs   (73.36 μs .. 156.5 μs)
+
+benchmarking foreignHash/cat.png
+time                 27.21 ms   (27.09 ms .. 27.47 ms)
+                     1.000 R²   (0.999 R² .. 1.000 R²)
+mean                 27.24 ms   (27.18 ms .. 27.37 ms)
+std dev              207.9 μs   (84.97 μs .. 311.8 μs)
+
+benchmarking foreignHash/frog.jpeg
+time                 12.81 ms   (12.78 ms .. 12.84 ms)
+                     1.000 R²   (1.000 R² .. 1.000 R²)
+mean                 12.87 ms   (12.85 ms .. 12.92 ms)
+std dev              80.81 μs   (56.17 μs .. 113.1 μs)
+
+benchmarking foreignHash/frog.png
+time                 14.03 ms   (13.94 ms .. 14.13 ms)
+                     1.000 R²   (1.000 R² .. 1.000 R²)
+mean                 13.95 ms   (13.93 ms .. 13.99 ms)
+std dev              79.36 μs   (52.02 μs .. 119.5 μs)
+```
+
+### Foreign Library
+
+This package contains a foreign library and header files.
diff --git a/include/hs_phash.h b/include/hs_phash.h
new file mode 100644
--- /dev/null
+++ b/include/hs_phash.h
@@ -0,0 +1,1 @@
+uint64_t hs_phash(const char *);
diff --git a/perceptual-hash.cabal b/perceptual-hash.cabal
--- a/perceptual-hash.cabal
+++ b/perceptual-hash.cabal
@@ -1,20 +1,21 @@
-cabal-version:   2.0
-name:            perceptual-hash
-version:         0.1.3.0
-license:         BSD3
-license-file:    LICENSE
-copyright:       Copyright: (c) 2019 Vanessa McHale
-maintainer:      vamchale@gmail.com
-author:          Vanessa McHale
-synopsis:        Find duplicate images
-description:     Find similar images using perceptual hashes
-category:        Application, CommandLine, Images
-build-type:      Simple
+cabal-version:      2.0
+name:               perceptual-hash
+version:            0.1.3.1
+license:            BSD3
+license-file:       LICENSE
+copyright:          Copyright: (c) 2019 Vanessa McHale
+maintainer:         vamchale@gmail.com
+author:             Vanessa McHale
+synopsis:           Find duplicate images
+description:        Find similar images using perceptual hashes
+category:           Application, CommandLine, Images
+build-type:         Simple
 data-files:
     demo-data/cat.png
     demo-data/frog.jpeg
     demo-data/frog.png
 
+extra-source-files: include/hs_phash.h
 extra-doc-files:
     README.md
     CHANGELOG.md
@@ -70,6 +71,7 @@
     hs-source-dirs:   foreign-src
     other-modules:    Export
     default-language: Haskell2010
+    install-includes: include/hs_phash.h
     ghc-options:      -Wall
     build-depends:
         base -any,
diff --git a/src/ForeignHash.hs b/src/ForeignHash.hs
--- a/src/ForeignHash.hs
+++ b/src/ForeignHash.hs
@@ -1,9 +1,10 @@
 -- N.B. this is a good deal faster than the Haskell code
 module ForeignHash ( foreignFileHash ) where
 
+import           Data.Coerce           (coerce)
 import           Data.Word             (Word64)
 import           Foreign.C.String      (CString, withCString)
-import           Foreign.C.Types       (CInt (..), CULLong)
+import           Foreign.C.Types       (CInt (..), CULLong (..))
 import           Foreign.Marshal.Alloc (alloca)
 import           Foreign.Ptr           (Ptr)
 import           Foreign.Storable      (peek)
@@ -16,7 +17,7 @@
     alloca $ \hashPtr -> do
         res <- ph_dct_imagehash cstr hashPtr
         check res
-        fromIntegral <$> peek hashPtr
+        coerce <$> peek hashPtr
 
     where check (-1) = error ("Hash of file " ++ fp ++ " failed.")
           check 0    = pure ()