diff --git a/src/Data/ByteString/Base64/Internal/Head.hs b/src/Data/ByteString/Base64/Internal/Head.hs
index 61d9c3d..85d49ad 100644
--- a/src/Data/ByteString/Base64/Internal/Head.hs
+++ b/src/Data/ByteString/Base64/Internal/Head.hs
@@ -1,6 +1,7 @@
 {-# LANGUAGE BangPatterns #-}
 {-# LANGUAGE CPP #-}
 {-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE ScopedTypeVariables #-}
 -- |
 -- Module       : Data.ByteString.Base64.Internal.Head
 -- Copyright    : (c) 2019-2022 Emily Pillmore
@@ -42,15 +43,28 @@ import GHC.Word
 import System.IO.Unsafe
 
 #ifdef SIMD
-import Foreign.C.Types (CSize, CChar)
+import Foreign.C.Types (CChar, CInt, CSize)
 import Foreign.Storable (peek)
 import qualified Foreign.Marshal.Utils as Foreign
+import qualified Data.Text as T
 import LibBase64Bindings
 #endif
 
 encodeBase64_ :: EncodingTable -> ByteString -> ByteString
 #ifdef SIMD
-encodeBase64_ _ (PS !sfp !soff !slen) =
+encodeBase64_ table b@(PS _ _ !slen)
+  | slen < threshold = encodeBase64Loop_ table b
+  | otherwise        = encodeBase64Simd_ b
+  where
+    !threshold = 1000 -- 1k
+#else
+encodeBase64_ table b = encodeBase64Loop_ table b
+#endif
+{-# inline encodeBase64_ #-}
+
+#ifdef SIMD
+encodeBase64Simd_ :: ByteString -> ByteString
+encodeBase64Simd_ (PS !sfp !soff !slen) =
   unsafeDupablePerformIO $ do
     dfp <- mallocPlainForeignPtrBytes dlen
     dlenFinal <- do
@@ -68,14 +82,10 @@ encodeBase64_ _ (PS !sfp !soff !slen) =
   where
     !dlen = 4 * ((slen + 2) `div` 3)
     !base64Flags = 0
+#endif
 
-    intToCSize :: Int -> CSize
-    intToCSize = fromIntegral
-
-    cSizeToInt :: CSize -> Int
-    cSizeToInt = fromIntegral
-#else
-encodeBase64_ (EncodingTable !aptr !efp) (PS !sfp !soff !slen) =
+encodeBase64Loop_ :: EncodingTable -> ByteString -> ByteString
+encodeBase64Loop_ (EncodingTable !aptr !efp) (PS !sfp !soff !slen) =
     unsafeDupablePerformIO $ do
       dfp <- mallocPlainForeignPtrBytes dlen
       withForeignPtr dfp $ \dptr ->
@@ -90,7 +100,6 @@ encodeBase64_ (EncodingTable !aptr !efp) (PS !sfp !soff !slen) =
             (loopTail dfp aptr dptr (castPtr end))
   where
     !dlen = 4 * ((slen + 2) `div` 3)
-#endif
 
 encodeBase64Nopad_ :: EncodingTable -> ByteString -> ByteString
 encodeBase64Nopad_ (EncodingTable !aptr !efp) (PS !sfp !soff !slen) =
@@ -109,6 +118,33 @@ encodeBase64Nopad_ (EncodingTable !aptr !efp) (PS !sfp !soff !slen) =
   where
     !dlen = 4 * ((slen + 2) `div` 3)
 
+#ifdef SIMD
+decodeBase64Simd_ :: ByteString -> IO (Either Text ByteString)
+decodeBase64Simd_ (PS !sfp !soff !slen) = do
+  withForeignPtr sfp $ \src -> do
+    dfp <- mallocPlainForeignPtrBytes dlen
+    edlenFinal :: Either Text CSize <- do
+      withForeignPtr dfp $ \out -> do
+        Foreign.with (intToCSize dlen) $ \outlen -> do
+          decodeResult <- base64_decode
+            (plusPtr (castPtr src :: Ptr CChar) soff)
+            (intToCSize slen)
+            out
+            outlen
+            base64Flags
+          case decodeResult of
+            1    -> Right <$> peek outlen
+            0    -> pure (Left "SIMD: Invalid input")
+            (-1) -> pure (Left "Invalid Codec")
+            x    -> pure (Left ("Unexpected result from libbase64 base64_decode: " <> T.pack (show (cIntToInt x))))
+    pure $ fmap
+      (\dlenFinal -> PS (castForeignPtr dfp) 0 (cSizeToInt dlenFinal))
+      edlenFinal
+  where
+    !dlen = (slen `quot` 4) * 3
+    !base64Flags = 0
+#endif
+
 -- | The main decode function. Takes a padding flag, a decoding table, and
 -- the input value, producing either an error string on the left, or a
 -- decoded value.
@@ -123,7 +159,22 @@ decodeBase64_
     :: ForeignPtr Word8
     -> ByteString
     -> IO (Either Text ByteString)
-decodeBase64_ !dtfp (PS !sfp !soff !slen) =
+#ifdef SIMD
+decodeBase64_ dtfp b@(PS _ _ !slen)
+  | slen < threshold = decodeBase64Loop_ dtfp b
+  | otherwise        = decodeBase64Simd_ b
+  where
+    !threshold = 250
+#else
+decodeBase64_ dtfp b = decodeBase64Loop_ dtfp b
+#endif
+{-# inline decodeBase64_ #-}
+
+decodeBase64Loop_
+    :: ForeignPtr Word8
+    -> ByteString
+    -> IO (Either Text ByteString)
+decodeBase64Loop_ !dtfp (PS !sfp !soff !slen) =
     withForeignPtr dtfp $ \dtable ->
     withForeignPtr sfp $ \sptr -> do
       dfp <- mallocPlainForeignPtrBytes dlen
@@ -134,7 +185,7 @@ decodeBase64_ !dtfp (PS !sfp !soff !slen) =
           dptr end dfp
   where
     !dlen = (slen `quot` 4) * 3
-{-# inline decodeBase64_ #-}
+{-# inline decodeBase64Loop_ #-}
 
 decodeBase64Lenient_ :: ForeignPtr Word8 -> ByteString -> ByteString
 decodeBase64Lenient_ !dtfp (PS !sfp !soff !slen) = unsafeDupablePerformIO $
@@ -150,3 +201,14 @@ decodeBase64Lenient_ !dtfp (PS !sfp !soff !slen) = unsafeDupablePerformIO $
           dfp
   where
     !dlen = ((slen + 3) `div` 4) * 3
+
+#ifdef SIMD
+intToCSize :: Int -> CSize
+intToCSize = fromIntegral
+
+cSizeToInt :: CSize -> Int
+cSizeToInt = fromIntegral
+
+cIntToInt :: CInt -> Int
+cIntToInt = fromIntegral
+#endif