diff --git a/plutus-core/plutus-core/src/PlutusCore/Compiler/Erase.hs b/plutus-core/plutus-core/src/PlutusCore/Compiler/Erase.hs
index 6dd766d58f8..947f510eae5 100644
--- a/plutus-core/plutus-core/src/PlutusCore/Compiler/Erase.hs
+++ b/plutus-core/plutus-core/src/PlutusCore/Compiler/Erase.hs
@@ -1,6 +1,6 @@
 module PlutusCore.Compiler.Erase (eraseTerm, eraseProgram) where
 
-import Data.Vector (fromList)
+import GHC.IsList (fromList)
 import PlutusCore.Core
 import PlutusCore.Name.Unique
 import UntypedPlutusCore.Core qualified as UPLC
diff --git a/plutus-core/untyped-plutus-core/src/UntypedPlutusCore/Core/Instance/Eq.hs b/plutus-core/untyped-plutus-core/src/UntypedPlutusCore/Core/Instance/Eq.hs
index 64d617ad9d0..28b42d76809 100644
--- a/plutus-core/untyped-plutus-core/src/UntypedPlutusCore/Core/Instance/Eq.hs
+++ b/plutus-core/untyped-plutus-core/src/UntypedPlutusCore/Core/Instance/Eq.hs
@@ -20,7 +20,7 @@ import PlutusCore.Rename.Monad
 import Universe
 
 import Data.Hashable
-import Data.Vector qualified as V
+import Data.Primitive.SmallArray (SmallArray)
 
 instance (GEq uni, Closed uni, uni `Everywhere` Eq, Eq fun, Eq ann) =>
             Eq (Term Name uni fun ann) where
@@ -37,7 +37,7 @@ type HashableTermConstraints uni fun ann =
 
 -- This instance is the only logical one, and exists also in the package `vector-instances`.
 -- Since this is the same implementation as that one, there isn't even much risk of incoherence.
-instance Hashable a => Hashable (V.Vector a) where
+instance Hashable a => Hashable (SmallArray a) where
   hashWithSalt s = hashWithSalt s . toList
 
 instance HashableTermConstraints uni fun ann => Hashable (Term Name uni fun ann)
diff --git a/plutus-core/untyped-plutus-core/src/UntypedPlutusCore/Core/Instance/Flat.hs b/plutus-core/untyped-plutus-core/src/UntypedPlutusCore/Core/Instance/Flat.hs
index 307163b5907..78cae9e1415 100644
--- a/plutus-core/untyped-plutus-core/src/UntypedPlutusCore/Core/Instance/Flat.hs
+++ b/plutus-core/untyped-plutus-core/src/UntypedPlutusCore/Core/Instance/Flat.hs
@@ -19,11 +19,11 @@ import UntypedPlutusCore.Core.Type
 
 import Control.Lens
 import Control.Monad
-import Data.Vector qualified as V
 import Flat
 import Flat.Decoder
 import Flat.Encoder
 import Flat.Encoder.Strict (sizeListWith)
+import GHC.IsList (fromList)
 import Universe
 
 {-
@@ -123,7 +123,7 @@ encodeTerm = \case
     Error    ann        -> encodeTermTag 6 <> encode ann
     Builtin  ann bn     -> encodeTermTag 7 <> encode ann <> encode bn
     Constr   ann i es   -> encodeTermTag 8 <> encode ann <> encode i <> encodeListWith encodeTerm es
-    Case     ann arg cs -> encodeTermTag 9 <> encode ann <> encodeTerm arg <> encodeListWith encodeTerm (V.toList cs)
+    Case     ann arg cs -> encodeTermTag 9 <> encode ann <> encodeTerm arg <> encodeListWith encodeTerm (toList cs)
 
 decodeTerm
     :: forall name uni fun ann
@@ -160,7 +160,7 @@ decodeTerm version builtinPred = go
             Constr   <$> decode <*> decode <*> decodeListWith go
         handleTerm 9 = do
             unless (version >= PLC.plcVersion110) $ fail $ "'case' is not allowed before version 1.1.0, this program has version: " ++ (show $ pretty version)
-            Case     <$> decode <*> go <*> (V.fromList <$> decodeListWith go)
+            Case     <$> decode <*> go <*> (fromList <$> decodeListWith go)
         handleTerm t = fail $ "Unknown term constructor tag: " ++ show t
 
 sizeTerm
@@ -188,7 +188,7 @@ sizeTerm tm sz =
     Error    ann        -> size ann sz'
     Builtin  ann bn     -> size ann $ size bn sz'
     Constr   ann i es   -> size ann $ size i $ sizeListWith sizeTerm es sz'
-    Case     ann arg cs -> size ann $ sizeTerm arg $ sizeListWith sizeTerm (V.toList cs) sz'
+    Case     ann arg cs -> size ann $ sizeTerm arg $ sizeListWith sizeTerm (toList cs) sz'
 
 -- | An encoder for programs.
 --
diff --git a/plutus-core/untyped-plutus-core/src/UntypedPlutusCore/Core/Instance/Scoping.hs b/plutus-core/untyped-plutus-core/src/UntypedPlutusCore/Core/Instance/Scoping.hs
index 043279c2662..9ae231d875e 100644
--- a/plutus-core/untyped-plutus-core/src/UntypedPlutusCore/Core/Instance/Scoping.hs
+++ b/plutus-core/untyped-plutus-core/src/UntypedPlutusCore/Core/Instance/Scoping.hs
@@ -15,7 +15,7 @@ import PlutusCore.Name.Unique
 import PlutusCore.Quote
 
 import Data.Proxy
-import Data.Vector qualified as Vector
+import GHC.IsList (fromList)
 
 firstBound :: Term name uni fun ann -> [name]
 firstBound (Apply _ (LamAbs _ name body) _) = name : firstBound body
@@ -41,7 +41,7 @@ instance name ~ Name => EstablishScoping (Term name uni fun) where
     establishScoping (Constr _ i es) = Constr NotAName <$> pure i <*> traverse establishScoping es
     establishScoping (Case _ a es) = do
         esScoped <- traverse establishScoping es
-        let esScopedPoked = addTheRest . map (\e -> (e, firstBound e)) $ Vector.toList esScoped
+        let esScopedPoked = addTheRest . map (\e -> (e, firstBound e)) $ toList esScoped
             branchBounds = map (snd . fst) esScopedPoked
             referenceInBranch ((branch, _), others) = referenceOutOfScope (map snd others) branch
         aScoped <- establishScoping a
@@ -49,7 +49,7 @@ instance name ~ Name => EstablishScoping (Term name uni fun) where
         -- in all the other ones, as well as outside of the whole case-expression. This is to check
         -- that none of the transformations leak variables outside of the branch they're bound in.
         pure . referenceOutOfScope branchBounds $
-            Case NotAName aScoped . Vector.fromList $ map referenceInBranch esScopedPoked
+            Case NotAName aScoped . fromList $ map referenceInBranch esScopedPoked
 
 instance name ~ Name => EstablishScoping (Program name uni fun) where
     establishScoping (Program _ ver term) = Program NotAName ver <$> establishScoping term
diff --git a/plutus-core/untyped-plutus-core/src/UntypedPlutusCore/Core/Type.hs b/plutus-core/untyped-plutus-core/src/UntypedPlutusCore/Core/Type.hs
index 9815d9b29fe..8710fe4f0b9 100644
--- a/plutus-core/untyped-plutus-core/src/UntypedPlutusCore/Core/Type.hs
+++ b/plutus-core/untyped-plutus-core/src/UntypedPlutusCore/Core/Type.hs
@@ -28,8 +28,9 @@ module UntypedPlutusCore.Core.Type
 import Control.Lens
 import PlutusPrelude
 
-import Data.Vector
+import Data.Primitive.SmallArray (SmallArray)
 import Data.Word
+import GHC.IsList (fromList)
 import PlutusCore.Builtin qualified as TPLC
 import PlutusCore.Core qualified as TPLC
 import PlutusCore.MkPlc
@@ -86,7 +87,7 @@ data Term name uni fun ann
     -- TODO: try spine-strict list or strict list or vector
     -- See Note [Constr tag type]
     | Constr !ann !Word64 ![Term name uni fun ann]
-    | Case !ann !(Term name uni fun ann) !(Vector (Term name uni fun ann))
+    | Case !ann !(Term name uni fun ann) {-# UNPACK #-} !(SmallArray (Term name uni fun ann))
     deriving stock (Functor, Generic)
 
 deriving stock instance (Show name, GShow uni, Everywhere uni Show, Show fun, Show ann, Closed uni)
diff --git a/plutus-core/untyped-plutus-core/src/UntypedPlutusCore/Core/Zip.hs b/plutus-core/untyped-plutus-core/src/UntypedPlutusCore/Core/Zip.hs
index 4d2ce01731c..8a7c8921978 100644
--- a/plutus-core/untyped-plutus-core/src/UntypedPlutusCore/Core/Zip.hs
+++ b/plutus-core/untyped-plutus-core/src/UntypedPlutusCore/Core/Zip.hs
@@ -10,7 +10,7 @@ module UntypedPlutusCore.Core.Zip
 
 import Control.Monad (void, when)
 import Control.Monad.Except (MonadError, throwError)
-import Data.Vector
+import GHC.IsList (fromList, toList)
 import UntypedPlutusCore.Core.Instance.Eq ()
 import UntypedPlutusCore.Core.Type
 
diff --git a/plutus-core/untyped-plutus-core/src/UntypedPlutusCore/Evaluation/Machine/Cek/Internal.hs b/plutus-core/untyped-plutus-core/src/UntypedPlutusCore/Evaluation/Machine/Cek/Internal.hs
index 7f710eb0877..cac214b6eef 100644
--- a/plutus-core/untyped-plutus-core/src/UntypedPlutusCore/Evaluation/Machine/Cek/Internal.hs
+++ b/plutus-core/untyped-plutus-core/src/UntypedPlutusCore/Evaluation/Machine/Cek/Internal.hs
@@ -96,15 +96,16 @@ import Data.DList qualified as DList
 import Data.Functor.Identity
 import Data.Hashable (Hashable)
 import Data.Kind qualified as GHC
+import Data.Primitive.SmallArray (SmallArray, indexSmallArray, sizeofSmallArray)
 import Data.Proxy
 import Data.Semigroup (stimes)
 import Data.Text (Text)
-import Data.Vector qualified as V
 import Data.Word
 import GHC.Generics
 import GHC.TypeLits
 import Prettyprinter
 import Universe
+import Unsafe.Coerce (unsafeCoerce)
 
 {- Note [Compilation peculiarities]
 READ THIS BEFORE TOUCHING ANYTHING IN THIS FILE
@@ -600,7 +601,7 @@ data Context uni fun ann
     -- See Note [Accumulators for terms]
     | FrameConstr !(CekValEnv uni fun ann) {-# UNPACK #-} !Word64 ![NTerm uni fun ann] !(ArgStack uni fun ann) !(Context uni fun ann)
     -- ^ @(constr i V0 ... Vj-1 _ Nj ... Nn)@
-    | FrameCases !(CekValEnv uni fun ann) !(V.Vector (NTerm uni fun ann)) !(Context uni fun ann)
+    | FrameCases !(CekValEnv uni fun ann) {-# UNPACK #-} !(SmallArray (NTerm uni fun ann)) !(Context uni fun ann)
     -- ^ @(case _ C0 .. Cn)@
     | NoFrame
 
@@ -775,16 +776,11 @@ enterComputeCek = computeCek
           []             -> returnCek ctx $ VConstr i done'
     -- s , case _ (C0 ... CN, ρ) ◅ constr i V1 .. Vm  ↦  s , [_ V1 ... Vm] ; ρ ▻ Ci
     returnCek (FrameCases env cs ctx) e = case e of
-        -- If the index is larger than the max bound of an Int, or negative, then it's a bad index
-        -- As it happens, this will currently never trigger, since i is a Word64, and the largest
-        -- Word64 value wraps to -1 as an Int64. So you can't wrap around enough to get an
-        -- "apparently good" value.
-        (VConstr i _) | fromIntegral @_ @Integer i > fromIntegral @Int @Integer maxBound ->
-                        throwingDischarged _MachineError (MissingCaseBranchMachineError i) e
-        -- Otherwise, we can safely convert the index to an Int and use it
-        (VConstr i args) -> case (V.!?) cs (fromIntegral i) of
-            Just t  -> computeCek (transferArgStack args ctx) env t
-            Nothing -> throwingDischarged _MachineError (MissingCaseBranchMachineError i) e
+        VConstr i args
+            | i < unsafeCoerce (sizeofSmallArray cs) ->
+                computeCek (transferArgStack args ctx) env . indexSmallArray cs $ unsafeCoerce i
+            | otherwise ->
+                throwingDischarged _MachineError (MissingCaseBranchMachineError i) e
         _ -> throwingDischarged _MachineError NonConstrScrutinizedMachineError e
 
     -- | Evaluate a 'HeadSpine' by pushing the arguments (if any) onto the stack and proceeding with
diff --git a/plutus-core/untyped-plutus-core/src/UntypedPlutusCore/Evaluation/Machine/SteppableCek/Internal.hs b/plutus-core/untyped-plutus-core/src/UntypedPlutusCore/Evaluation/Machine/SteppableCek/Internal.hs
index 0d795d334f3..824addd0db1 100644
--- a/plutus-core/untyped-plutus-core/src/UntypedPlutusCore/Evaluation/Machine/SteppableCek/Internal.hs
+++ b/plutus-core/untyped-plutus-core/src/UntypedPlutusCore/Evaluation/Machine/SteppableCek/Internal.hs
@@ -57,11 +57,11 @@ import UntypedPlutusCore.Evaluation.Machine.Cek.StepCounter
 import Control.Lens hiding (Context)
 import Control.Monad
 import Control.Monad.Primitive
+import Data.Primitive.SmallArray (SmallArray)
 import Data.Proxy
 import Data.RandomAccessList.Class qualified as Env
 import Data.Semigroup (stimes)
 import Data.Text (Text)
-import Data.Vector qualified as V
 import Data.Word (Word64)
 import GHC.TypeNats
 import Universe
@@ -100,7 +100,7 @@ data Context uni fun ann
     | FrameAwaitFunValue ann !(CekValue uni fun ann) !(Context uni fun ann)
     | FrameForce ann !(Context uni fun ann)                                               -- ^ @(force _)@
     | FrameConstr ann !(CekValEnv uni fun ann) {-# UNPACK #-} !Word64 ![NTerm uni fun ann] !(ArgStack uni fun ann) !(Context uni fun ann)
-    | FrameCases ann !(CekValEnv uni fun ann) !(V.Vector (NTerm uni fun ann)) !(Context uni fun ann)
+    | FrameCases ann !(CekValEnv uni fun ann) !(SmallArray (NTerm uni fun ann)) !(Context uni fun ann)
     | NoFrame
 
 deriving stock instance (GShow uni, Everywhere uni Show, Show fun, Show ann, Closed uni)
@@ -206,7 +206,7 @@ returnCek (FrameCases ann env cs ctx) e = case e of
     -- "apparently good" value.
     (VConstr i _) | fromIntegral @_ @Integer i > fromIntegral @Int @Integer maxBound ->
                     throwingDischarged _MachineError (MissingCaseBranchMachineError i) e
-    (VConstr i args) -> case (V.!?) cs (fromIntegral i) of
+    (VConstr i args) -> case toList cs ^? ix (fromIntegral i) of
         Just t  ->
               let ctx' = transferArgStack ann args ctx
               in computeCek ctx' env t
diff --git a/plutus-core/untyped-plutus-core/src/UntypedPlutusCore/Parser.hs b/plutus-core/untyped-plutus-core/src/UntypedPlutusCore/Parser.hs
index 91fb56d29a2..6c9c704ed9d 100644
--- a/plutus-core/untyped-plutus-core/src/UntypedPlutusCore/Parser.hs
+++ b/plutus-core/untyped-plutus-core/src/UntypedPlutusCore/Parser.hs
@@ -28,7 +28,7 @@ import UntypedPlutusCore.Core.Type qualified as UPLC
 import UntypedPlutusCore.Rename (Rename (rename))
 
 import Data.Text (Text)
-import Data.Vector qualified as V
+import GHC.IsList (fromList)
 import PlutusCore.Error (AsParserErrorBundle)
 import PlutusCore.MkPlc (mkIterApp)
 import PlutusCore.Parser hiding (parseProgram, parseTerm, program)
@@ -82,7 +82,7 @@ constrTerm = withSpan $ \sp ->
 caseTerm :: Parser PTerm
 caseTerm = withSpan $ \sp ->
     inParens $ do
-      res <- UPLC.Case sp <$> (symbol "case" *> term) <*> (V.fromList <$> many term)
+      res <- UPLC.Case sp <$> (symbol "case" *> term) <*> (fromList <$> many term)
       whenVersion (\v -> v < plcVersion110) $ fail "'case' is not allowed before version 1.1.0"
       pure res
 
diff --git a/plutus-core/untyped-plutus-core/src/UntypedPlutusCore/Transform/CaseReduce.hs b/plutus-core/untyped-plutus-core/src/UntypedPlutusCore/Transform/CaseReduce.hs
index d17a44236ae..0f205e6126d 100644
--- a/plutus-core/untyped-plutus-core/src/UntypedPlutusCore/Transform/CaseReduce.hs
+++ b/plutus-core/untyped-plutus-core/src/UntypedPlutusCore/Transform/CaseReduce.hs
@@ -9,8 +9,8 @@ import UntypedPlutusCore.Core
 import UntypedPlutusCore.Transform.Simplifier (SimplifierStage (CaseReduce), SimplifierT,
                                                recordSimplification)
 
-import Control.Lens (transformOf)
-import Data.Vector qualified as V
+import Control.Lens (ix, transformOf, (^?))
+import Data.Foldable (toList)
 
 caseReduce
     :: Monad m
@@ -23,6 +23,6 @@ caseReduce term = do
 
 processTerm :: Term name uni fun a -> Term name uni fun a
 processTerm = \case
-    Case ann (Constr _ i args) cs | Just c <- (V.!?) cs (fromIntegral i) ->
+    Case ann (Constr _ i args) cs | Just c <- toList cs ^? ix (fromIntegral i) ->
                                     mkIterApp c ((ann,) <$> args)
     t                                                     -> t
diff --git a/plutus-core/untyped-plutus-core/test/Generators.hs b/plutus-core/untyped-plutus-core/test/Generators.hs
index 791ab327c4c..af7f0635076 100644
--- a/plutus-core/untyped-plutus-core/test/Generators.hs
+++ b/plutus-core/untyped-plutus-core/test/Generators.hs
@@ -6,7 +6,7 @@
 -- | UPLC property tests (pretty-printing\/parsing and binary encoding\/decoding).
 module Generators where
 
-import PlutusPrelude (display, fold, on, void, zipExact, (&&&))
+import PlutusPrelude (display, fold, on, toList, void, zipExact, (&&&))
 
 import PlutusCore (Name, _nameText)
 import PlutusCore.Annotation
@@ -28,7 +28,6 @@ import UntypedPlutusCore.Parser (parseProgram, parseTerm)
 import Control.Lens (view)
 import Data.Text (Text)
 import Data.Text qualified as T
-import Data.Vector qualified as V
 
 import Hedgehog (annotate, annotateShow, failure, property, tripping, (===))
 import Hedgehog.Gen qualified as Gen
@@ -61,7 +60,7 @@ compareTerm (Delay _ t ) (Delay _ t')         = compareTerm t t'
 compareTerm (Constant _ x) (Constant _ y)     = x == y
 compareTerm (Builtin _ bi) (Builtin _ bi')    = bi == bi'
 compareTerm (Constr _ i es) (Constr _ i' es') = i == i' && maybe False (all (uncurry compareTerm)) (zipExact es es')
-compareTerm (Case _ arg cs) (Case _ arg' cs') = compareTerm arg arg' && maybe False (all (uncurry compareTerm)) (zipExact (V.toList cs) (V.toList cs'))
+compareTerm (Case _ arg cs) (Case _ arg' cs') = compareTerm arg arg' && maybe False (all (uncurry compareTerm)) (zipExact (toList cs) (toList cs'))
 compareTerm (Error _ ) (Error _ )             = True
 compareTerm _ _                               = False
 
diff --git a/plutus-core/untyped-plutus-core/test/Transform/CaseOfCase/Test.hs b/plutus-core/untyped-plutus-core/test/Transform/CaseOfCase/Test.hs
index f942dd431f7..18397162573 100644
--- a/plutus-core/untyped-plutus-core/test/Transform/CaseOfCase/Test.hs
+++ b/plutus-core/untyped-plutus-core/test/Transform/CaseOfCase/Test.hs
@@ -6,7 +6,7 @@ module Transform.CaseOfCase.Test where
 
 import Data.ByteString.Lazy qualified as BSL
 import Data.Text.Encoding (encodeUtf8)
-import Data.Vector qualified as V
+import GHC.IsList (fromList)
 import PlutusCore qualified as PLC
 import PlutusCore.Evaluation.Machine.BuiltinCostModel (BuiltinCostModel)
 import PlutusCore.Evaluation.Machine.ExBudgetingDefaults (defaultBuiltinCostModelForTesting,
@@ -45,7 +45,7 @@ caseOfCase1 = runQuote do
   let ite = Force () (Builtin () PLC.IfThenElse)
       true = Constr () 0 []
       false = Constr () 1 []
-      alts = V.fromList [mkConstant @Integer () 1, mkConstant @Integer () 2]
+      alts = fromList [mkConstant @Integer () 1, mkConstant @Integer () 2]
   pure $ Case () (mkIterApp ite [((), Var () b), ((), true), ((), false)]) alts
 
 {- | This should not simplify, because one of the branches of `ifThenElse` is not a `Constr`.
@@ -59,7 +59,7 @@ caseOfCase2 = runQuote do
   let ite = Force () (Builtin () PLC.IfThenElse)
       true = Var () t
       false = Constr () 1 []
-      alts = V.fromList [mkConstant @Integer () 1, mkConstant @Integer () 2]
+      alts = fromList [mkConstant @Integer () 1, mkConstant @Integer () 2]
   pure $ Case () (mkIterApp ite [((), Var () b), ((), true), ((), false)]) alts
 
 {- | Similar to `caseOfCase1`, but the type of the @true@ and @false@ branches is
@@ -76,7 +76,7 @@ caseOfCase3 = runQuote do
       false = Constr () 1 []
       altTrue = Var () f
       altFalse = mkConstant @Integer () 2
-      alts = V.fromList [altTrue, altFalse]
+      alts = fromList [altTrue, altFalse]
   pure $ Case () (mkIterApp ite [((), Var () b), ((), true), ((), false)]) alts
 
 {- |
@@ -107,7 +107,7 @@ caseOfCaseWithError =
         , ((), Constr () 1 []) -- False
         ]
     )
-    (V.fromList [mkConstant @() () (), Error ()])
+    (fromList [mkConstant @() () (), Error ()])
 
 testCaseOfCaseWithError :: TestTree
 testCaseOfCaseWithError =
diff --git a/plutus-core/untyped-plutus-core/test/Transform/Simplify.hs b/plutus-core/untyped-plutus-core/test/Transform/Simplify.hs
index e5b2e770e10..d84d11b3b58 100644
--- a/plutus-core/untyped-plutus-core/test/Transform/Simplify.hs
+++ b/plutus-core/untyped-plutus-core/test/Transform/Simplify.hs
@@ -4,7 +4,7 @@
 module Transform.Simplify where
 
 import Data.Text (Text)
-import Data.Vector qualified as V
+import GHC.IsList (fromList)
 import PlutusCore qualified as PLC
 import PlutusCore.MkPlc (mkConstant, mkIterApp, mkIterAppNoAnn)
 import PlutusCore.Quote (Quote, freshName, runQuote)
@@ -34,7 +34,7 @@ caseOfCase1 = runQuote $ do
   let ite = Force () (Builtin () PLC.IfThenElse)
       true = Constr () 0 []
       false = Constr () 1 []
-      alts = V.fromList [mkConstant @Integer () 1, mkConstant @Integer () 2]
+      alts = fromList [mkConstant @Integer () 1, mkConstant @Integer () 2]
   pure $ Case () (mkIterApp ite [((), Var () b), ((), true), ((), false)]) alts
 
 {- | This should not simplify, because one of the branches of `ifThenElse` is not a `Constr`.
@@ -48,7 +48,7 @@ caseOfCase2 = runQuote $ do
   let ite = Force () (Builtin () PLC.IfThenElse)
       true = Var () t
       false = Constr () 1 []
-      alts = V.fromList [mkConstant @Integer () 1, mkConstant @Integer () 2]
+      alts = fromList [mkConstant @Integer () 1, mkConstant @Integer () 2]
   pure $ Case () (mkIterApp ite [((), Var () b), ((), true), ((), false)]) alts
 
 {- | Similar to `caseOfCase1`, but the type of the @true@ and @false@ branches is
@@ -65,7 +65,7 @@ caseOfCase3 = runQuote $ do
       false = Constr () 1 []
       altTrue = Var () f
       altFalse = mkConstant @Integer () 2
-      alts = V.fromList [altTrue, altFalse]
+      alts = fromList [altTrue, altFalse]
   pure $ Case () (mkIterApp ite [((), Var () b), ((), true), ((), false)]) alts
 
 -- | The `Delay` should be floated into the lambda.
@@ -408,7 +408,7 @@ cse1 = runQuote $ do
       branch1 = plus onePlusTwoPlusX threePlusX
       branch2 = plus twoPlusX threePlusX
       branch3 = fourPlusX
-      caseExpr = Case () (Var () y) (V.fromList [branch1, branch2, branch3])
+      caseExpr = Case () (Var () y) (fromList [branch1, branch2, branch3])
   pure $ LamAbs () x (LamAbs () y body)
 
 -- | This is the second example in Note [CSE].