diff --git a/CHANGELOG b/CHANGELOG
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,5 +1,8 @@
 # Changelog
 
+- 0.3.1 (2026-02-01)
+  * Adds SPECIALIZE pragmas for IO and ST to improve the generated Core.
+
 - 0.3.0 (2026-02-01)
   * This backwards-incompatible version changes the "bring your own HMAC
     function" design and simply provides specialized DRBGs for
diff --git a/bench/Weight.hs b/bench/Weight.hs
--- a/bench/Weight.hs
+++ b/bench/Weight.hs
@@ -22,9 +22,6 @@
 instance NFData (DRBG512.DRBG s) where
   rnf d = d `seq` ()
 
-instance NFData DRBG512.Error where
-  rnf e = e `seq` ()
-
 main :: IO ()
 main = do
   !drbg256 <- DRBG256.new mempty mempty mempty
diff --git a/lib/Crypto/DRBG/HMAC/SHA256.hs b/lib/Crypto/DRBG/HMAC/SHA256.hs
--- a/lib/Crypto/DRBG/HMAC/SHA256.hs
+++ b/lib/Crypto/DRBG/HMAC/SHA256.hs
@@ -1,10 +1,11 @@
+{-# OPTIONS_HADDOCK prune #-}
 {-# LANGUAGE BangPatterns #-}
 {-# LANGUAGE MagicHash #-}
 {-# LANGUAGE PatternSynonyms #-}
 {-# LANGUAGE UnboxedTuples #-}
 
 -- |
--- Module: Crypto.DRBG.HMAC
+-- Module: Crypto.DRBG.HMAC.SHA256
 -- Copyright: (c) 2024 Jared Tobin
 -- License: MIT
 -- Maintainer: Jared Tobin <jared@ppad.tech>
@@ -33,6 +34,8 @@
 import Crypto.Hash.SHA256.Internal (Registers(..))
 import qualified Crypto.Hash.SHA256.Internal as SHA256 (cat)
 import Control.Monad.Primitive (PrimMonad, PrimState)
+import Control.Monad.ST (ST)
+import GHC.Exts (RealWorld)
 import qualified Control.Monad.Primitive as Prim (unsafeIOToPrim)
 import Data.Bits ((.<<.), (.>>.), (.|.))
 import qualified Data.ByteString as BS
@@ -87,6 +90,10 @@
   update drbg (entropy <> nonce <> ps)
   pure $! DRBG drbg
 {-# INLINABLE new #-}
+{-# SPECIALIZE new
+  :: BS.ByteString -> BS.ByteString -> BS.ByteString -> IO (DRBG RealWorld) #-}
+{-# SPECIALIZE new
+  :: BS.ByteString -> BS.ByteString -> BS.ByteString -> ST s (DRBG s) #-}
 
 -- | Reseed a DRBG.
 --
@@ -160,13 +167,19 @@
         !(GHC.Word.W32# v05) <- PA.readPrimArray drbg 15
         !(GHC.Word.W32# v06) <- PA.readPrimArray drbg 16
         !(GHC.Word.W32# v07) <- PA.readPrimArray drbg 17
-        let !k0  = Registers (# k00, k01, k02, k03, k04, k05, k06, k07 #)
-            !v0  = Registers (# v00, v01, v02, v03, v04, v05, v06, v07 #)
+        let !k0 = Registers (# k00, k01, k02, k03, k04, k05, k06, k07 #)
+            !v0 = Registers (# v00, v01, v02, v03, v04, v05, v06, v07 #)
         !res <- gen_loop drbg k0 v0 bytes
         update drbg addl
         write_counter drbg (ctr + 1)
         pure $! Right res
 {-# INLINABLE gen #-}
+{-# SPECIALIZE gen
+  :: DRBG RealWorld -> BS.ByteString -> Word64
+  -> IO (Either Error BS.ByteString) #-}
+{-# SPECIALIZE gen
+  :: DRBG s -> BS.ByteString -> Word64
+  -> ST s (Either Error BS.ByteString) #-}
 
 -- | Wipe the state of a DRBG.
 --
@@ -287,6 +300,10 @@
     let !k2 = Registers (# k20, k21, k22, k23, k24, k25, k26, k27 #)
     Prim.unsafeIOToPrim $ SHA256._hmac_rr vp sp k2 v1
 {-# INLINABLE update #-}
+{-# SPECIALIZE update
+  :: PA.MutablePrimArray RealWorld Word32 -> BS.ByteString -> IO () #-}
+{-# SPECIALIZE update
+  :: PA.MutablePrimArray s Word32 -> BS.ByteString -> ST s () #-}
 
 init_counter
   :: PrimMonad m
diff --git a/lib/Crypto/DRBG/HMAC/SHA512.hs b/lib/Crypto/DRBG/HMAC/SHA512.hs
--- a/lib/Crypto/DRBG/HMAC/SHA512.hs
+++ b/lib/Crypto/DRBG/HMAC/SHA512.hs
@@ -1,3 +1,4 @@
+{-# OPTIONS_HADDOCK prune #-}
 {-# LANGUAGE BangPatterns #-}
 {-# LANGUAGE MagicHash #-}
 {-# LANGUAGE PatternSynonyms #-}
@@ -33,6 +34,8 @@
 import Crypto.Hash.SHA512.Internal (Registers(..))
 import qualified Crypto.Hash.SHA512.Internal as SHA512 (cat)
 import Control.Monad.Primitive (PrimMonad, PrimState)
+import Control.Monad.ST (ST)
+import GHC.Exts (RealWorld)
 import qualified Control.Monad.Primitive as Prim (unsafeIOToPrim)
 import qualified Data.ByteString as BS
 import qualified Data.ByteString.Builder as BSB
@@ -87,6 +90,10 @@
   update drbg (entropy <> nonce <> ps)
   pure $! DRBG drbg
 {-# INLINABLE new #-}
+{-# SPECIALIZE new
+  :: BS.ByteString -> BS.ByteString -> BS.ByteString -> IO (DRBG RealWorld) #-}
+{-# SPECIALIZE new
+  :: BS.ByteString -> BS.ByteString -> BS.ByteString -> ST s (DRBG s) #-}
 
 -- | Reseed a DRBG.
 --
@@ -167,6 +174,12 @@
         write_counter drbg (ctr + 1)
         pure $! Right res
 {-# INLINABLE gen #-}
+{-# SPECIALIZE gen
+  :: DRBG RealWorld -> BS.ByteString -> Word64
+  -> IO (Either Error BS.ByteString) #-}
+{-# SPECIALIZE gen
+  :: DRBG s -> BS.ByteString -> Word64
+  -> ST s (Either Error BS.ByteString) #-}
 
 -- | Wipe the state of a DRBG.
 --
@@ -282,6 +295,10 @@
     let !k2 = Registers (# k20, k21, k22, k23, k24, k25, k26, k27 #)
     Prim.unsafeIOToPrim $ SHA512._hmac_rr vp sp k2 v1
 {-# INLINABLE update #-}
+{-# SPECIALIZE update
+  :: PA.MutablePrimArray RealWorld Word64 -> BS.ByteString -> IO () #-}
+{-# SPECIALIZE update
+  :: PA.MutablePrimArray s Word64 -> BS.ByteString -> ST s () #-}
 
 init_counter
   :: PrimMonad m
diff --git a/ppad-hmac-drbg.cabal b/ppad-hmac-drbg.cabal
--- a/ppad-hmac-drbg.cabal
+++ b/ppad-hmac-drbg.cabal
@@ -1,6 +1,6 @@
 cabal-version:      3.0
 name:               ppad-hmac-drbg
-version:            0.3.0
+version:            0.3.1
 synopsis:           HMAC-based deterministic random bit generator
 license:            MIT
 license-file:       LICENSE