diff --git a/programs/vest_api/src/vest_processor.rs b/programs/vest_api/src/vest_processor.rs
index 321002bac..2ed760d47 100644
--- a/programs/vest_api/src/vest_processor.rs
+++ b/programs/vest_api/src/vest_processor.rs
@@ -10,6 +10,7 @@ use solana_config_api::get_config_data;
 use solana_sdk::{
     account::{Account, KeyedAccount},
     instruction::InstructionError,
+    instruction_processor_utils::next_keyed_account,
     pubkey::Pubkey,
 };
 
@@ -58,6 +59,7 @@ pub fn process_instruction(
     keyed_accounts: &mut [KeyedAccount],
     data: &[u8],
 ) -> Result<(), InstructionError> {
+    let keyed_accounts_iter = &mut keyed_accounts.iter_mut();
     let instruction = deserialize(data).map_err(|_| InstructionError::InvalidInstructionData)?;
 
     match instruction {
@@ -68,10 +70,7 @@ pub fn process_instruction(
             date_pubkey,
             total_lamports,
         } => {
-            let contract_keyed_account = match keyed_accounts {
-                [ka0] => ka0,
-                _ => return Err(InstructionError::InvalidArgument),
-            };
+            let contract_keyed_account = next_keyed_account(keyed_accounts_iter)?;
             let contract_account = &mut contract_keyed_account.account;
             let vest_state = VestState {
                 terminator_pubkey,
@@ -84,10 +83,8 @@ pub fn process_instruction(
             vest_state.serialize(&mut contract_account.data)
         }
         VestInstruction::SetPayee(payee_pubkey) => {
-            let (contract_keyed_account, old_payee_keyed_account) = match keyed_accounts {
-                [ka0, ka1] => (ka0, ka1),
-                _ => return Err(InstructionError::InvalidArgument),
-            };
+            let contract_keyed_account = next_keyed_account(keyed_accounts_iter)?;
+            let old_payee_keyed_account = next_keyed_account(keyed_accounts_iter)?;
             let contract_account = &mut contract_keyed_account.account;
             let mut vest_state = VestState::deserialize(&contract_account.data)?;
             parse_signed_account(old_payee_keyed_account, &vest_state.payee_pubkey)?;
@@ -95,11 +92,9 @@ pub fn process_instruction(
             vest_state.serialize(&mut contract_account.data)
         }
         VestInstruction::RedeemTokens => {
-            let (contract_keyed_account, date_keyed_account, payee_keyed_account) =
-                match keyed_accounts {
-                    [ka0, ka1, ka2] => (ka0, ka1, ka2),
-                    _ => return Err(InstructionError::InvalidArgument),
-                };
+            let contract_keyed_account = next_keyed_account(keyed_accounts_iter)?;
+            let date_keyed_account = next_keyed_account(keyed_accounts_iter)?;
+            let payee_keyed_account = next_keyed_account(keyed_accounts_iter)?;
             let contract_account = &mut contract_keyed_account.account;
             let mut vest_state = VestState::deserialize(&contract_account.data)?;
             let current_date = parse_date_account(date_keyed_account, &vest_state.date_pubkey)?;
@@ -109,12 +104,9 @@ pub fn process_instruction(
             vest_state.serialize(&mut contract_account.data)
         }
         VestInstruction::Terminate => {
-            let (contract_keyed_account, terminator_keyed_account, payee_keyed_account) =
-                match keyed_accounts {
-                    [ka0, ka1] => (ka0, ka1, None),
-                    [ka0, ka1, ka2] => (ka0, ka1, Some(ka2)),
-                    _ => return Err(InstructionError::InvalidArgument),
-                };
+            let contract_keyed_account = next_keyed_account(keyed_accounts_iter)?;
+            let terminator_keyed_account = next_keyed_account(keyed_accounts_iter)?;
+            let payee_keyed_account = keyed_accounts_iter.next();
             let contract_account = &mut contract_keyed_account.account;
             let mut vest_state = VestState::deserialize(&contract_account.data)?;
             let terminator_account =
@@ -335,7 +327,7 @@ mod tests {
                 .send_message(&[&alice_keypair], message)
                 .unwrap_err()
                 .unwrap(),
-            TransactionError::InstructionError(1, InstructionError::InvalidArgument)
+            TransactionError::InstructionError(1, InstructionError::NotEnoughAccountKeys)
         );
     }
 
diff --git a/sdk/src/instruction.rs b/sdk/src/instruction.rs
index 026c89d60..cf8b55de6 100644
--- a/sdk/src/instruction.rs
+++ b/sdk/src/instruction.rs
@@ -67,6 +67,9 @@ pub enum InstructionError {
     /// Rent_epoch account changed, but shouldn't have
     RentEpochModified,
 
+    /// The instruction expected additional account keys
+    NotEnoughAccountKeys,
+
     /// CustomError allows on-chain programs to implement program-specific error types and see
     /// them returned by the Solana runtime. A CustomError may be any type that is represented
     /// as or serialized to a u32 integer.
diff --git a/sdk/src/instruction_processor_utils.rs b/sdk/src/instruction_processor_utils.rs
index 853d7b8e0..8da5eafbc 100644
--- a/sdk/src/instruction_processor_utils.rs
+++ b/sdk/src/instruction_processor_utils.rs
@@ -38,6 +38,11 @@ where
     }
 }
 
+/// Return the next KeyedAccount or a NotEnoughAccountKeys instruction error
+pub fn next_keyed_account<I: Iterator>(iter: &mut I) -> Result<I::Item, InstructionError> {
+    iter.next().ok_or(InstructionError::NotEnoughAccountKeys)
+}
+
 pub trait DecodeError<E> {
     fn decode_custom_error_to_enum(custom: u32) -> Option<E>
     where