diff --git a/crucible-llvm/crucible-llvm.cabal b/crucible-llvm/crucible-llvm.cabal
index 6b3c24b5f..528fcfd8a 100644
--- a/crucible-llvm/crucible-llvm.cabal
+++ b/crucible-llvm/crucible-llvm.cabal
@@ -73,6 +73,7 @@ library
     Lang.Crucible.LLVM.Extension
     Lang.Crucible.LLVM.Globals
     Lang.Crucible.LLVM.Intrinsics
+    Lang.Crucible.LLVM.Intrinsics.Cast
     Lang.Crucible.LLVM.Intrinsics.Libc
     Lang.Crucible.LLVM.Intrinsics.LLVM
     Lang.Crucible.LLVM.MalformedLLVMModule
diff --git a/crucible-llvm/src/Lang/Crucible/LLVM/Intrinsics/Cast.hs b/crucible-llvm/src/Lang/Crucible/LLVM/Intrinsics/Cast.hs
new file mode 100644
index 000000000..4f9f35e7e
--- /dev/null
+++ b/crucible-llvm/src/Lang/Crucible/LLVM/Intrinsics/Cast.hs
@@ -0,0 +1,120 @@
+-- |
+-- Module           : Lang.Crucible.LLVM.Intrinsics.Cast
+-- Description      : Cast between bitvectors and pointers in signatures
+-- Copyright        : (c) Galois, Inc 2024
+-- License          : BSD3
+-- Maintainer       : Langston Barrett <langston@galois.com>
+-- Stability        : provisional
+--
+-- The built-in overrides in "Lang.Crucible.LLVM.Intrinsics.Libc" and
+-- "Lang.Crucible.LLVM.Intrinsics.LLVM" frequently take arguments of type
+-- 'Lang.Crucible.Types.BVType', but at runtime everything is represented as an
+-- 'Lang.Crucible.LLVM.MemModel.Pointer.LLVMPtr'. This module contains helpers
+-- for \"casting\" between pointers and bitvectors.
+------------------------------------------------------------------------
+
+{-# LANGUAGE GADTs #-}
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE RankNTypes #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+
+module Lang.Crucible.LLVM.Intrinsics.Cast
+  ( ValCastError
+  , printValCastError
+  , ArgCast(applyArgCast)
+  , ValCast(applyValCast)
+  , castLLVMArgs
+  , castLLVMRet
+  ) where
+
+import           Control.Monad.IO.Class (liftIO)
+import           Control.Lens
+
+import qualified Data.Parameterized.Context as Ctx
+import           Data.Parameterized.Some (Some(Some))
+import           Data.Parameterized.TraversableFC (fmapFC)
+
+import           Lang.Crucible.Backend
+import           Lang.Crucible.Simulator.OverrideSim
+import           Lang.Crucible.Simulator.RegMap
+import           Lang.Crucible.Types
+
+import           Lang.Crucible.LLVM.MemModel
+
+data ValCastError
+  = -- | Mismatched number of arguments ('castLLVMArgs') or struct fields
+    -- ('castLLVMRet').
+    MismatchedShape
+    -- | Can\'t cast between these types
+  | ValCastError (Some TypeRepr) (Some TypeRepr)
+
+-- | Turn a 'ValCastError' into a human-readable message (lines).
+printValCastError :: ValCastError -> [String]
+printValCastError =
+  \case
+    MismatchedShape -> ["argument shape mismatch"]
+    ValCastError (Some ret) (Some ret') ->
+      [ "Cannot cast types"
+      , "*** Source type: " ++ show ret
+      , "*** Target type: " ++ show ret'
+      ]
+
+-- | A function to (infallibly) cast between 'Ctx.Assignment's of 'RegEntry's.
+newtype ArgCast p sym ext args args' =
+  ArgCast { applyArgCast :: (forall rtp l a.
+    Ctx.Assignment (RegEntry sym) args ->
+    OverrideSim p sym ext rtp l a (Ctx.Assignment (RegEntry sym) args')) }
+
+-- | A function to (infallibly) cast a value of types @tp@ to @tp'@.
+newtype ValCast p sym ext tp tp' =
+  ValCast { applyValCast :: (forall rtp l a.
+    RegValue sym tp ->
+    OverrideSim p sym ext rtp l a (RegValue sym tp')) }
+
+-- | Attempt to construct a function to cast between 'Ctx.Assignment's of
+-- 'RegEntry's.
+castLLVMArgs :: forall p sym ext bak args args'.
+  IsSymBackend sym bak =>
+  bak ->
+  CtxRepr args' ->
+  CtxRepr args ->
+  Either ValCastError (ArgCast p sym ext args args')
+castLLVMArgs _ Ctx.Empty Ctx.Empty =
+  Right (ArgCast (\_ -> return Ctx.Empty))
+castLLVMArgs bak (rest' Ctx.:> tp') (rest Ctx.:> tp) =
+  do ValCast f  <- castLLVMRet bak tp tp'
+     ArgCast fs <- castLLVMArgs bak rest' rest
+     Right (ArgCast
+              (\(xs Ctx.:> x) -> do
+                    xs' <- fs xs
+                    x'  <- f (regValue x)
+                    pure (xs' Ctx.:> RegEntry tp' x')))
+castLLVMArgs _ _ _ = Left MismatchedShape
+
+-- | Attempt to construct a function to cast values of type @ret@ to type
+-- @ret'@.
+castLLVMRet ::
+  IsSymBackend sym bak =>
+  bak ->
+  TypeRepr ret  ->
+  TypeRepr ret' ->
+  Either ValCastError (ValCast p sym ext ret ret')
+castLLVMRet bak (BVRepr w) (LLVMPointerRepr w')
+  | Just Refl <- testEquality w w'
+  = Right (ValCast (liftIO . llvmPointer_bv (backendGetSym bak)))
+castLLVMRet bak (LLVMPointerRepr w) (BVRepr w')
+  | Just Refl <- testEquality w w'
+  = Right (ValCast (liftIO . projectLLVM_bv bak))
+castLLVMRet bak (VectorRepr tp) (VectorRepr tp')
+  = do ValCast f <- castLLVMRet bak tp tp'
+       Right (ValCast (traverse f))
+castLLVMRet bak (StructRepr ctx) (StructRepr ctx')
+  = do ArgCast tf <- castLLVMArgs bak ctx' ctx
+       Right (ValCast (\vals ->
+          let vals' = Ctx.zipWith (\tp (RV v) -> RegEntry tp v) ctx vals in
+          fmapFC (\x -> RV (regValue x)) <$> tf vals'))
+
+castLLVMRet _bak ret ret'
+  | Just Refl <- testEquality ret ret'
+  = Right (ValCast return)
+castLLVMRet _bak ret ret' = Left (ValCastError (Some ret) (Some ret'))
diff --git a/crucible-llvm/src/Lang/Crucible/LLVM/Intrinsics/Common.hs b/crucible-llvm/src/Lang/Crucible/LLVM/Intrinsics/Common.hs
index a5d29a591..07e1eb489 100644
--- a/crucible-llvm/src/Lang/Crucible/LLVM/Intrinsics/Common.hs
+++ b/crucible-llvm/src/Lang/Crucible/LLVM/Intrinsics/Common.hs
@@ -58,7 +58,6 @@ import qualified System.Info as Info
 import qualified ABI.Itanium as ABI
 import qualified Data.Parameterized.Context as Ctx
 import           Data.Parameterized.Some (Some(..))
-import           Data.Parameterized.TraversableFC (fmapFC)
 
 import           Lang.Crucible.Backend
 import           Lang.Crucible.CFG.Common (GlobalVar)
@@ -78,6 +77,7 @@ import           Lang.Crucible.LLVM.Eval (callStackFromMemVar)
 import           Lang.Crucible.LLVM.Globals (registerFunPtr)
 import           Lang.Crucible.LLVM.MemModel
 import           Lang.Crucible.LLVM.MemModel.CallStack (CallStack)
+import qualified Lang.Crucible.LLVM.Intrinsics.Cast as Cast
 import           Lang.Crucible.LLVM.Translation.Monad
 import           Lang.Crucible.LLVM.Translation.Types
 
@@ -199,74 +199,6 @@ apply this special case to other override functions (e.g.,
 ------------------------------------------------------------------------
 -- ** register_llvm_override
 
-newtype ArgTransformer p sym ext args args' =
-  ArgTransformer { applyArgTransformer :: (forall rtp l a.
-    Ctx.Assignment (RegEntry sym) args ->
-    OverrideSim p sym ext rtp l a (Ctx.Assignment (RegEntry sym) args')) }
-
-newtype ValTransformer p sym ext tp tp' =
-  ValTransformer { applyValTransformer :: (forall rtp l a.
-    RegValue sym tp ->
-    OverrideSim p sym ext rtp l a (RegValue sym tp')) }
-
-transformLLVMArgs :: forall m p sym ext bak args args'.
-  (IsSymBackend sym bak, Monad m, HasLLVMAnn sym) =>
-  -- | This function name is only used in panic messages.
-  FunctionName ->
-  bak ->
-  CtxRepr args' ->
-  CtxRepr args ->
-  m (ArgTransformer p sym ext args args')
-transformLLVMArgs _fnName _ Ctx.Empty Ctx.Empty =
-  return (ArgTransformer (\_ -> return Ctx.Empty))
-transformLLVMArgs fnName bak (rest' Ctx.:> tp') (rest Ctx.:> tp) = do
-  return (ArgTransformer
-           (\(xs Ctx.:> x) ->
-              do (ValTransformer f)  <- transformLLVMRet fnName bak tp tp'
-                 (ArgTransformer fs) <- transformLLVMArgs fnName bak rest' rest
-                 xs' <- fs xs
-                 x'  <- RegEntry tp' <$> f (regValue x)
-                 pure (xs' Ctx.:> x')))
-transformLLVMArgs fnName _ _ _ =
-  panic "Intrinsics.transformLLVMArgs"
-    [ "transformLLVMArgs: argument shape mismatch!"
-    , "in function: " ++ Text.unpack (functionName fnName)
-    ]
-
-transformLLVMRet ::
-  (IsSymBackend sym bak, Monad m, HasLLVMAnn sym) =>
-  -- | This function name is only used in panic messages.
-  FunctionName ->
-  bak ->
-  TypeRepr ret  ->
-  TypeRepr ret' ->
-  m (ValTransformer p sym ext ret ret')
-transformLLVMRet _fnName bak (BVRepr w) (LLVMPointerRepr w')
-  | Just Refl <- testEquality w w'
-  = return (ValTransformer (liftIO . llvmPointer_bv (backendGetSym bak)))
-transformLLVMRet _fnName bak (LLVMPointerRepr w) (BVRepr w')
-  | Just Refl <- testEquality w w'
-  = return (ValTransformer (liftIO . projectLLVM_bv bak))
-transformLLVMRet fnName bak (VectorRepr tp) (VectorRepr tp')
-  = do ValTransformer f <- transformLLVMRet fnName bak tp tp'
-       return (ValTransformer (traverse f))
-transformLLVMRet fnName bak (StructRepr ctx) (StructRepr ctx')
-  = do ArgTransformer tf <- transformLLVMArgs fnName bak ctx' ctx
-       return (ValTransformer (\vals ->
-          let vals' = Ctx.zipWith (\tp (RV v) -> RegEntry tp v) ctx vals in
-          fmapFC (\x -> RV (regValue x)) <$> tf vals'))
-
-transformLLVMRet _fnName _bak ret ret'
-  | Just Refl <- testEquality ret ret'
-  = return (ValTransformer return)
-transformLLVMRet fnName _bak ret ret'
-  = panic "Intrinsics.transformLLVMRet"
-      [ "Cannot transform types"
-      , "*** Source type: " ++ show ret
-      , "*** Target type: " ++ show ret'
-      , "in function: " ++ Text.unpack (functionName fnName)
-      ]
-
 -- | Do some pipe-fitting to match a Crucible override function into the shape
 --   expected by the LLVM calling convention.  This basically just coerces
 --   between values of @BVType w@ and values of @LLVMPointerType w@.
@@ -283,11 +215,23 @@ build_llvm_override ::
   OverrideSim p sym ext rtp l a (Override p sym ext args' ret')
 build_llvm_override fnm args ret args' ret' llvmOverride =
   ovrWithBackend $ \bak ->
-  do fargs <- transformLLVMArgs fnm bak args args'
-     fret  <- transformLLVMRet fnm bak ret  ret'
+  do fargs <-
+       case Cast.castLLVMArgs bak args args' of
+         Left err ->
+           panic "Intrinsics.build_llvm_override"
+             (Cast.printValCastError err ++
+               [ "in function: " ++ Text.unpack (functionName fnm) ])
+         Right f -> pure f
+     fret <-
+       case Cast.castLLVMRet bak ret ret' of
+         Left err ->
+           panic "Intrinsics.build_llvm_override"
+             (Cast.printValCastError err ++
+               [ "in function: " ++ Text.unpack (functionName fnm) ])
+         Right f -> pure f
      return $ mkOverride' fnm ret' $
             do RegMap xs <- getOverrideArgs
-               applyValTransformer fret =<< llvmOverride =<< applyArgTransformer fargs xs
+               Cast.applyValCast fret =<< llvmOverride =<< Cast.applyArgCast fargs xs
 
 polymorphic1_llvm_override :: forall p sym arch wptr l a rtp.
   (IsSymInterface sym, HasLLVMAnn sym, HasPtrWidth wptr) =>