diff --git a/core/src/sigverify.rs b/core/src/sigverify.rs
index 1d56939e68..225befe908 100644
--- a/core/src/sigverify.rs
+++ b/core/src/sigverify.rs
@@ -497,8 +497,6 @@ mod tests {
         let fee = 2;
         let blockhash = Hash::default();
 
-        let keys = vec![keypair0.pubkey(), keypair1.pubkey()];
-
         let system_instruction = SystemInstruction::Move { lamports };
 
         let program_ids = vec![system_program::id(), solana_budget_api::id()];
@@ -507,7 +505,7 @@ mod tests {
 
         let tx = Transaction::new_with_instructions(
             &keypairs,
-            &keys,
+            &[],
             blockhash,
             fee,
             program_ids,
diff --git a/runtime/src/bank.rs b/runtime/src/bank.rs
index d3454394db..3d5077fbc3 100644
--- a/runtime/src/bank.rs
+++ b/runtime/src/bank.rs
@@ -1246,7 +1246,13 @@ mod tests {
         let res = bank.process_transactions(&vec![tx.clone()]);
         assert_eq!(res.len(), 1);
         assert_eq!(bank.get_balance(&key1.pubkey()), 1);
-        res[0].clone().unwrap_err();
+
+        // TODO: Why do we convert errors to Oks?
+        //res[0].clone().unwrap_err();
+
+        bank.get_signature_status(&tx.signatures[0])
+            .unwrap()
+            .unwrap_err();
     }
 
     fn new_from_parent(parent: &Arc<Bank>) -> Bank {
diff --git a/runtime/src/runtime.rs b/runtime/src/runtime.rs
index 9232da3b0d..527c7b117e 100644
--- a/runtime/src/runtime.rs
+++ b/runtime/src/runtime.rs
@@ -138,25 +138,28 @@ pub fn has_duplicates<T: PartialEq>(xs: &[T]) -> bool {
 }
 
 /// Get mut references to a subset of elements.
-fn get_subset_unchecked_mut<'a, T>(xs: &'a mut [T], indexes: &[u8]) -> Vec<&'a mut T> {
+fn get_subset_unchecked_mut<'a, T>(
+    xs: &'a mut [T],
+    indexes: &[u8],
+) -> Result<Vec<&'a mut T>, InstructionError> {
     // Since the compiler doesn't know the indexes are unique, dereferencing
     // multiple mut elements is assumed to be unsafe. If, however, all
     // indexes are unique, it's perfectly safe. The returned elements will share
     // the liftime of the input slice.
 
-    // Make certain there are no duplicate indexes. If there are, panic because we
-    // can't return multiple mut references to the same element.
+    // Make certain there are no duplicate indexes. If there are, return an error
+    // because we can't return multiple mut references to the same element.
     if has_duplicates(indexes) {
-        panic!("duplicate indexes");
+        return Err(InstructionError::DuplicateAccountIndex);
     }
 
-    indexes
+    Ok(indexes
         .iter()
         .map(|i| {
             let ptr = &mut xs[*i as usize] as *mut T;
             unsafe { &mut *ptr }
         })
-        .collect()
+        .collect())
 }
 
 /// Execute a transaction.
@@ -170,7 +173,8 @@ pub fn execute_transaction(
 ) -> Result<(), TransactionError> {
     for (instruction_index, instruction) in tx.instructions.iter().enumerate() {
         let executable_accounts = &mut (&mut loaders[instruction.program_ids_index as usize]);
-        let mut program_accounts = get_subset_unchecked_mut(tx_accounts, &instruction.accounts);
+        let mut program_accounts = get_subset_unchecked_mut(tx_accounts, &instruction.accounts)
+            .map_err(|err| TransactionError::InstructionError(instruction_index as u8, err))?;
         execute_instruction(
             tx,
             instruction_index,
@@ -197,7 +201,7 @@ where
         tx_accounts.push(Account::new(0, 0, &system_program::id()));
     }
     for (i, ix) in tx.instructions.iter().enumerate() {
-        let mut ix_accounts = get_subset_unchecked_mut(tx_accounts, &ix.accounts);
+        let mut ix_accounts = get_subset_unchecked_mut(tx_accounts, &ix.accounts).unwrap();
         let mut keyed_accounts: Vec<_> = ix
             .accounts
             .iter()
@@ -244,25 +248,30 @@ mod tests {
 
     #[test]
     fn test_get_subset_unchecked_mut() {
-        assert_eq!(get_subset_unchecked_mut(&mut [7, 8], &[0]), vec![&mut 7]);
         assert_eq!(
-            get_subset_unchecked_mut(&mut [7, 8], &[0, 1]),
+            get_subset_unchecked_mut(&mut [7, 8], &[0]).unwrap(),
+            vec![&mut 7]
+        );
+        assert_eq!(
+            get_subset_unchecked_mut(&mut [7, 8], &[0, 1]).unwrap(),
             vec![&mut 7, &mut 8]
         );
     }
 
     #[test]
-    #[should_panic]
     fn test_get_subset_unchecked_mut_duplicate_index() {
         // This panics, because it assumes duplicate detection is done elsewhere.
-        get_subset_unchecked_mut(&mut [7, 8], &[0, 0]);
+        assert_eq!(
+            get_subset_unchecked_mut(&mut [7, 8], &[0, 0]).unwrap_err(),
+            InstructionError::DuplicateAccountIndex
+        );
     }
 
     #[test]
     #[should_panic]
     fn test_get_subset_unchecked_mut_out_of_bounds() {
         // This panics, because it assumes bounds validation is done elsewhere.
-        get_subset_unchecked_mut(&mut [7, 8], &[2]);
+        get_subset_unchecked_mut(&mut [7, 8], &[2]).unwrap();
     }
 
     #[test]
diff --git a/sdk/src/transaction.rs b/sdk/src/transaction.rs
index f7c1fad956..2fd4fe453e 100644
--- a/sdk/src/transaction.rs
+++ b/sdk/src/transaction.rs
@@ -35,6 +35,9 @@ pub enum InstructionError {
 
     /// Program modified the data of an account that doesn't belong to it
     ExternalAccountDataModified,
+
+    /// An account was referenced more than once in a single instruction
+    DuplicateAccountIndex,
 }
 
 impl InstructionError {
@@ -177,7 +180,7 @@ impl Transaction {
             Hash::default(),
             fee,
         );
-        transaction.sign(&[from_keypair], recent_blockhash);
+        transaction.sign_checked(&[from_keypair], recent_blockhash);
         transaction
     }
     pub fn new_unsigned<T: Serialize>(
@@ -219,14 +222,14 @@ impl Transaction {
             .collect();
         account_keys.extend_from_slice(keys);
         let mut tx = Transaction {
-            signatures: vec![],
+            signatures: Vec::with_capacity(from_keypairs.len()),
             account_keys,
             recent_blockhash: Hash::default(),
             fee,
             program_ids,
             instructions,
         };
-        tx.sign(from_keypairs, recent_blockhash);
+        tx.sign_checked(from_keypairs, recent_blockhash);
         tx
     }
     pub fn data(&self, instruction_index: usize) -> &[u8] {