diff --git a/solana/solitaire/program/src/error.rs b/solana/solitaire/program/src/error.rs
index fd4d150fb..aa38774ce 100644
--- a/solana/solitaire/program/src/error.rs
+++ b/solana/solitaire/program/src/error.rs
@@ -12,6 +12,9 @@ pub type ErrBox = Box<dyn std::error::Error>;
 /// There are several places in Solitaire that might fail, we want descriptive errors.
 #[derive(Debug)]
 pub enum SolitaireError {
+    /// The AccountInfo parser expected a mutable key where a readonly was found, or vice versa.
+    InvalidMutability(Pubkey),
+
     /// The AccountInfo parser expected a Signer, but the account did not sign.
     InvalidSigner(Pubkey),
 
diff --git a/solana/solitaire/program/src/processors/peel.rs b/solana/solitaire/program/src/processors/peel.rs
index b1c173042..60ebd1f14 100644
--- a/solana/solitaire/program/src/processors/peel.rs
+++ b/solana/solitaire/program/src/processors/peel.rs
@@ -62,6 +62,26 @@ impl<'a, 'b: 'a, 'c, T: Peel<'a, 'b, 'c>, const Seed: &'static str> Peel<'a, 'b,
     }
 }
 
+/// Peel a Mutable key.
+impl<'a, 'b: 'a, 'c, T: Peel<'a, 'b, 'c>> Peel<'a, 'b, 'c> for Mut<T>
+{
+    fn peel<I>(mut ctx: &'c mut Context<'a, 'b, 'c, I>) -> Result<Self> {
+        ctx.immutable = false;
+        match ctx.info().is_writable {
+            true => T::peel(ctx).map(|v| Mut(v)),
+            _ => Err(SolitaireError::InvalidMutability(*ctx.info().key).into()),
+        }
+    }
+
+    fn deps() -> Vec<Pubkey> {
+        T::deps()
+    }
+
+    fn persist(&self, program_id: &Pubkey) -> Result<()> {
+        T::persist(self, program_id)
+    }
+}
+
 /// Peel a Signer.
 impl<'a, 'b: 'a, 'c, T: Peel<'a, 'b, 'c>> Peel<'a, 'b, 'c> for Signer<T> {
     fn peel<I>(ctx: &'c mut Context<'a, 'b, 'c, I>) -> Result<Self> {
@@ -126,6 +146,10 @@ where
 /// calls here.
 impl<'a, 'b: 'a, 'c> Peel<'a, 'b, 'c> for Info<'b> {
     fn peel<I>(ctx: &'c mut Context<'a, 'b, 'c, I>) -> Result<Self> {
+        if ctx.immutable && ctx.info().is_writable {
+            return Err(SolitaireError::InvalidMutability(*ctx.info().key).into());
+        }
+
         Ok(ctx.info().clone())
     }
     fn deps() -> Vec<Pubkey> {
@@ -147,6 +171,10 @@ impl<
     > Peel<'a, 'b, 'c> for Data<'b, T, IsInitialized>
 {
     fn peel<I>(ctx: &'c mut Context<'a, 'b, 'c, I>) -> Result<Self> {
+        if ctx.immutable && ctx.info().is_writable {
+            return Err(SolitaireError::InvalidMutability(*ctx.info().key).into());
+        }
+
         // If we're initializing the type, we should emit system/rent as deps.
         let (initialized, data): (bool, T) = match IsInitialized {
             AccountState::Uninitialized => {
diff --git a/solana/solitaire/program/src/types/context.rs b/solana/solitaire/program/src/types/context.rs
index 1bd556894..4908e9744 100644
--- a/solana/solitaire/program/src/types/context.rs
+++ b/solana/solitaire/program/src/types/context.rs
@@ -14,22 +14,29 @@ pub struct Context<'a, 'b: 'a, 'c, T> {
     /// A reference to the program_id of the current program.
     pub this: &'a Pubkey,
 
+    /// A reference to the instructions account list, one or more keys may be extracted during
+    /// the peeling process.
     pub iter: &'c mut Iter<'a, AccountInfo<'b>>,
 
-    /// This is a reference to the instruction data we are processing this
-    /// account for.
+    /// Reference to the data passed to the current instruction.
     pub data: &'a T,
 
+    /// An optional account info for this Peelable item, some fields may be other structures that
+    /// do not themselves have an account info associated with the field.
     pub info: Option<&'a AccountInfo<'b>>,
+
+    /// Whether to enforce immutability.
+    pub immutable: bool,
 }
 
 impl<'a, 'b: 'a, 'c, T> Context<'a, 'b, 'c, T> {
     pub fn new(program: &'a Pubkey, iter: &'c mut Iter<'a, AccountInfo<'b>>, data: &'a T) -> Self {
         Context {
             this: program,
+            info: None,
+            immutable: true,
             iter,
             data,
-            info: None,
         }
     }
 
diff --git a/solana/solitaire/program/src/types/layers.rs b/solana/solitaire/program/src/types/layers.rs
index d55768474..5fb48b2e1 100644
--- a/solana/solitaire/program/src/types/layers.rs
+++ b/solana/solitaire/program/src/types/layers.rs
@@ -23,6 +23,9 @@ use borsh::{
     BorshSerialize,
 };
 
+#[repr(transparent)]
+pub struct Mut<Next>(pub Next);
+
 #[repr(transparent)]
 pub struct Signer<Next>(pub Next);
 
@@ -48,6 +51,19 @@ impl<T> DerefMut for Signer<T> {
     }
 }
 
+impl<T> Deref for Mut<T> {
+    type Target = T;
+    fn deref(&self) -> &Self::Target {
+        unsafe { std::mem::transmute(&self.0) }
+    }
+}
+
+impl<T> DerefMut for Mut<T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        unsafe { std::mem::transmute(&mut self.0) }
+    }
+}
+
 impl<T> Deref for System<T> {
     type Target = T;
     fn deref(&self) -> &Self::Target {