diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,8 @@
+# 1.0.0.0
+
+  * `compressFile` now takes block size
+  * Add `compressFileDefault`
+
 # 0.1.0.1
 
 * Fix bug compressing files that are not large
diff --git a/bz3.cabal b/bz3.cabal
--- a/bz3.cabal
+++ b/bz3.cabal
@@ -1,6 +1,6 @@
 cabal-version:      3.4
 name:               bz3
-version:            0.1.0.1
+version:            1.0.0.0
 synopsis:           High-level bindings to bz3
 description:
     Streaming compression/decompression in bz3 format via lazy bytestrings
@@ -22,7 +22,7 @@
 
 common warnings
     ghc-options:
-        -Wall -fno-warn-missing-signatures -Wno-x-partial
+        -Wall -fno-warn-missing-signatures
         -Wincomplete-uni-patterns -Wincomplete-record-updates
         -Wredundant-constraints -Wmissing-export-lists -Wcpp-undef
         -Wunused-packages -Wno-operator-whitespace-ext-conflict
@@ -56,5 +56,6 @@
         bz3,
         bytestring,
         directory >=1.2.5.0,
+        random >=1.0.0,
         tasty,
         tasty-hunit
diff --git a/src/Codec/Bz3.hs b/src/Codec/Bz3.hs
--- a/src/Codec/Bz3.hs
+++ b/src/Codec/Bz3.hs
@@ -1,6 +1,7 @@
 module Codec.Bz3 ( Bz3Error (..)
                  , decompressFile
                  , compressFile
+                 , compressFileDefault
                  ) where
 
 import           Codec.Bz3.Binary
@@ -33,9 +34,14 @@
     loop st bs | BSL.null bs = pure []
                | otherwise = do {(dc, rest) <- decN st bs; (dc:) <$> loop st rest}
 
+-- | @since 1.0.0.0
+compressFileDefault :: BSL.ByteString -> BSL.ByteString
+compressFileDefault = compressFile (16*1024*1024)
+
 -- will fail if bz3st cannot fit exotic big input
-compressFile :: BSL.ByteString -> BSL.ByteString
-compressFile d = LazyST.runST $ do
+compressFile :: Int32 -- ^ Block size, 65kB to 511MB
+             -> BSL.ByteString -> BSL.ByteString
+compressFile ibSz d = LazyST.runST $ do
     st <- LazyST.unsafeIOToST $ newBz3StForeign bSz
     (sz,bb) <- loop st (BSL.toChunks d)
     let fileH = runPut (putFileH sz)
@@ -53,7 +59,7 @@
     feed=fromIntegral (bz3Bound bSz)
 
     bSz :: Integral a => a
-    bSz=16*1024*1024
+    bSz=fromIntegral ibSz
 
 encN :: ForeignPtr Bz3St -> BS.ByteString -> LazyST.ST s (Int32, BS.ByteString)
 encN st inp = LazyST.unsafeIOToST $
@@ -68,12 +74,12 @@
 decN :: ForeignPtr Bz3St -> BSL.ByteString -> LazyST.ST s (BS.ByteString, BSL.ByteString)
 decN st inp = LazyST.unsafeIOToST $ do
     let (next, off, Chunk csz osz) = y (runGetOrFail getChunk inp)
+        bb=BSL.toStrict (BSL.drop 8 $ BSL.take off inp)
     if osz>=64
         then do
             let bufSz = bz3Bound (fromIntegral osz)
                 csz32 = fromIntegral csz; osz32 = fromIntegral osz
             buf <- mallocForeignPtrBytes (fromIntegral bufSz)
-            let bb=BSL.toStrict (BSL.drop 8 $ BSL.take off inp)
             res <- withForeignPtr buf $ \b -> do
                 BS.unsafeUseAsCStringLen bb $ \(p,isz) -> copyArray b (castPtr p) isz
                 bz3DecodeBlock st b bufSz csz32 osz32
@@ -82,7 +88,6 @@
                 Left e | e==Bz3Ok -> pure ()
                        | otherwise -> error =<< bz3Strerror st
             pure (BS.BS (castForeignPtr buf) (fromIntegral osz), next)
-        else let bb=BSL.toStrict (BSL.drop 8 $ BSL.take off inp)
-             in pure (bb, next)
+        else pure (bb, next)
   where
     y (Right x) = x; y (Left (_, _, e)) = error e
diff --git a/test/Main.hs b/test/Main.hs
--- a/test/Main.hs
+++ b/test/Main.hs
@@ -3,6 +3,7 @@
 import           Codec.Bz3
 import qualified Data.ByteString.Lazy as BSL
 import           System.Directory     (doesDirectoryExist, listDirectory)
+import           System.Random        (randomRIO)
 import           Test.Tasty           (defaultMain, testGroup)
 import           Test.Tasty.HUnit     (assertBool, testCase)
 
@@ -13,7 +14,9 @@
 
 roundtrip fp = testCase ("roundtrip " ++ fp) $ do
     contents <- BSL.readFile fp
-    let d = decompressFile contents
-        e = compressFile d
+    eb <- randomRIO (2::Int,8)
+    let bsz=2^eb*1024*1024
+        d = decompressFile contents
+        e = compressFile bsz d
         d1 = decompressFile e
     assertBool "doesn't error" (d1 `seq` True)