diff --git a/src/Data/Text/Builder/Linear/Dec/Unbounded.hs b/src/Data/Text/Builder/Linear/Dec/Unbounded.hs
index 93c7708..02cc74f 100644
--- a/src/Data/Text/Builder/Linear/Dec/Unbounded.hs
+++ b/src/Data/Text/Builder/Linear/Dec/Unbounded.hs
@@ -5,8 +5,8 @@
 module Data.Text.Builder.Linear.Dec.Unbounded (
   (|>$$),
   ($$<|),
-  prependUnboundedDecimal,
-  Strategy (..),
+  -- prependUnboundedDecimal,
+  -- Strategy (..),
 )
 where
 
@@ -345,40 +345,40 @@ padWithZeros ∷ ∀ s. A.MArray s → Int → Int → ST s ()
 padWithZeros marr off count = unsafeReplicate marr off count 0x30
 {-# INLINE padWithZeros #-}
 
+--------------------------------------------------------------------------------
+-- For testing purpose only
 --------------------------------------------------------------------------------
 
--- FIXME: for testing purpose only
-
-prependUnboundedDecimal ∷ Integral a ⇒ Strategy → a → Buffer ⊸ Buffer
-prependUnboundedDecimal strategy n buffer = case toInteger n of
-  !n' →
-    prependBounded'
-      (maxIntegerDecLen n')
-      (\dst dstOff → unsafePrependDec' strategy dst dstOff n')
-      buffer
-
-unsafePrependDec' ∷ ∀ s. Strategy → A.MArray s → Int → Integer → ST s Int
-unsafePrependDec' s marr off@(I# off#) n' = case n' of
-  I.IS i# → Bounded.unsafePrependDec marr off (I# i#)
-  _ → unsafePrependBigNatDec' s marr (off# -# 1#) (integerToBigNat# n') >>= prependSign
-    where
-      prependSign !off' =
-        if n' < 0
-          then do
-            A.unsafeWrite marr (off' - 1) 0x2d -- '-'
-            pure (off - off' + 1)
-          else pure (off - off')
-{-# INLINEABLE unsafePrependDec' #-}
-
-unsafePrependBigNatDec' ∷ ∀ s. Strategy → A.MArray s → DigitsWriter s
-unsafePrependBigNatDec' strategy marr !off0 !n0
-  | BN.bigNatSize n0 < bigSizeThreshold = prependSmallNat marr off0 n0
-  | BN.bigNatSize n0 < hugeSizeThreshold = prependBigNat marr off0 n0
-  | otherwise = prependHugeNat marr off0 n0
-  where
-    bigSizeThreshold, hugeSizeThreshold ∷ Word
-    !(bigSizeThreshold, hugeSizeThreshold) = case strategy of
-      SmallOnly → (maxBound, maxBound)
-      BigOnly → (minBound, maxBound)
-      HugeOnly → (minBound, minBound)
-      Optimum → (25, 400)
+-- prependUnboundedDecimal ∷ Integral a ⇒ Strategy → a → Buffer ⊸ Buffer
+-- prependUnboundedDecimal strategy n buffer = case toInteger n of
+--   !n' →
+--     prependBounded'
+--       (maxIntegerDecLen n')
+--       (\dst dstOff → unsafePrependDec' strategy dst dstOff n')
+--       buffer
+
+-- unsafePrependDec' ∷ ∀ s. Strategy → A.MArray s → Int → Integer → ST s Int
+-- unsafePrependDec' s marr off@(I# off#) n' = case n' of
+--   I.IS i# → Bounded.unsafePrependDec marr off (I# i#)
+--   _ → unsafePrependBigNatDec' s marr (off# -# 1#) (integerToBigNat# n') >>= prependSign
+--     where
+--       prependSign !off' =
+--         if n' < 0
+--           then do
+--             A.unsafeWrite marr (off' - 1) 0x2d -- '-'
+--             pure (off - off' + 1)
+--           else pure (off - off')
+-- {-# INLINEABLE unsafePrependDec' #-}
+
+-- unsafePrependBigNatDec' ∷ ∀ s. Strategy → A.MArray s → DigitsWriter s
+-- unsafePrependBigNatDec' strategy marr !off0 !n0
+--   | BN.bigNatSize n0 < bigSizeThreshold = prependSmallNat marr off0 n0
+--   | BN.bigNatSize n0 < hugeSizeThreshold = prependBigNat marr off0 n0
+--   | otherwise = prependHugeNat marr off0 n0
+--   where
+--     bigSizeThreshold, hugeSizeThreshold ∷ Word
+--     !(bigSizeThreshold, hugeSizeThreshold) = case strategy of
+--       SmallOnly → (maxBound, maxBound)
+--       BigOnly → (minBound, maxBound)
+--       HugeOnly → (minBound, minBound)
+--       Optimum → (25, 400)