diff --git a/CHANGELOG b/CHANGELOG
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,3 +1,7 @@
+2024-07-07
+        * Version bump (3.20). (#522)
+        * Update Op2, Struct to support struct field updates. (#520)
+
 2024-05-07
         * Version bump (3.19.1). (#512)
 
diff --git a/copilot-core.cabal b/copilot-core.cabal
--- a/copilot-core.cabal
+++ b/copilot-core.cabal
@@ -1,6 +1,6 @@
 cabal-version:       >=1.10
 name:                copilot-core
-version:             3.19.1
+version:             3.20
 synopsis:            An intermediate representation for Copilot.
 description:
   Intermediate representation for Copilot.
diff --git a/src/Copilot/Core/Operators.hs b/src/Copilot/Core/Operators.hs
--- a/src/Copilot/Core/Operators.hs
+++ b/src/Copilot/Core/Operators.hs
@@ -13,9 +13,10 @@
   where
 
 -- External imports
-import Data.Bits    (Bits)
-import Data.Word    (Word32)
-import GHC.TypeLits (KnownSymbol)
+import Data.Bits     (Bits)
+import Data.Typeable (Typeable)
+import Data.Word     (Word32)
+import GHC.TypeLits  (KnownSymbol)
 
 -- Internal imports
 import Copilot.Core.Type       (Field (..), Type (..))
@@ -95,6 +96,11 @@
   -- Array operator.
   Index    :: Type (Array n t) -> Op2 (Array n t) Word32 t
               -- ^ Array access/projection of an array element.
+
+  -- Struct operator.
+  UpdateField :: (Typeable b, KnownSymbol s, Show b)
+              => Type a -> Type b -> (a -> Field s b) -> Op2 a b a
+              -- ^ Update a field of a struct.
 
 -- | Ternary operators.
 data Op3 a b c d where
diff --git a/src/Copilot/Core/Type.hs b/src/Copilot/Core/Type.hs
--- a/src/Copilot/Core/Type.hs
+++ b/src/Copilot/Core/Type.hs
@@ -34,6 +34,7 @@
     , Struct
     , fieldName
     , accessorName
+    , updateField
     )
   where
 
@@ -58,6 +59,9 @@
 
   -- | Transforms all the struct's fields into a list of values.
   toValues :: a -> [Value a]
+
+  updateField :: a -> Value t -> a
+  updateField = error "Field updates not supported for this type."
 
 -- | The field of a struct, together with a representation of its type.
 data Value a =