diff --git a/plutus-ledger-api/plutus-ledger-api.cabal b/plutus-ledger-api/plutus-ledger-api.cabal
index 662f40594d8..a6fdb6c5b02 100644
--- a/plutus-ledger-api/plutus-ledger-api.cabal
+++ b/plutus-ledger-api/plutus-ledger-api.cabal
@@ -109,6 +109,7 @@ library
   build-depends:
     , aeson
     , aeson-pretty
+    , array
     , base               >=4.9   && <5
     , base16-bytestring  >=1
     , bytestring
diff --git a/plutus-ledger-api/src/PlutusLedgerApi/Common/SerialisedScript.hs b/plutus-ledger-api/src/PlutusLedgerApi/Common/SerialisedScript.hs
index dd8853dbada..741be5ce2e9 100644
--- a/plutus-ledger-api/src/PlutusLedgerApi/Common/SerialisedScript.hs
+++ b/plutus-ledger-api/src/PlutusLedgerApi/Common/SerialisedScript.hs
@@ -45,7 +45,8 @@ import Control.Monad.Except (MonadError)
 import Data.ByteString.Lazy qualified as BSL
 import Data.ByteString.Short
 import Data.Coerce
-import Data.Set as Set
+import Data.Array.ST (newArray, runSTUArray, writeArray)
+import Data.Array.Unboxed (UArray, (!))
 import GHC.Generics
 import NoThunks.Class
 import Prettyprinter
@@ -197,10 +198,14 @@ scriptCBORDecoder
   -> CBOR.Decoder s ScriptNamedDeBruijn
 scriptCBORDecoder ll pv =
   -- See Note [New builtins/language versions and protocol versions]
-  let availableBuiltins = builtinsAvailableIn ll pv
+  let available = builtinsAvailableIn ll pv
+      availableArr :: UArray DefaultFun Bool
+      availableArr = runSTUArray $ do
+        arr <- newArray (minBound, maxBound) False
+        mapM_ (\f -> writeArray arr f True) available
+        return arr
       flatDecoder = UPLC.decodeProgram checkBuiltin
-      -- TODO: optimize this by using a better datastructure e.g. 'IntSet'
-      checkBuiltin f | f `Set.member` availableBuiltins = Nothing
+      checkBuiltin f | availableArr ! f = Nothing
       checkBuiltin f =
         Just $
           "Builtin function "