diff --git a/programs/bpf/benches/bpf_loader.rs b/programs/bpf/benches/bpf_loader.rs
index 316f821c7c..355af8603a 100644
--- a/programs/bpf/benches/bpf_loader.rs
+++ b/programs/bpf/benches/bpf_loader.rs
@@ -80,7 +80,7 @@ fn bench_program_alu(bencher: &mut Bencher) {
 
     println!("Interpreted:");
     assert_eq!(
-        1, /*true*/
+        0, /*success*/
         vm.execute_program(&mut inner_iter, &[], &[]).unwrap()
     );
     assert_eq!(ARMSTRONG_LIMIT, LittleEndian::read_u64(&inner_iter));
@@ -106,7 +106,7 @@ fn bench_program_alu(bencher: &mut Bencher) {
     // vm.jit_compile().unwrap();
     // unsafe {
     //     assert_eq!(
-    //         1, /*true*/
+    //         0, /*success*/
     //         vm.execute_program_jit(&mut inner_iter).unwrap()
     //     );
     // }
diff --git a/programs/bpf/c/src/bench_alu/bench_alu.c b/programs/bpf/c/src/bench_alu/bench_alu.c
index d34a245260..870c67f2eb 100644
--- a/programs/bpf/c/src/bench_alu/bench_alu.c
+++ b/programs/bpf/c/src/bench_alu/bench_alu.c
@@ -6,7 +6,7 @@
 
 #include <solana_sdk.h>
 
-extern bool entrypoint(const uint8_t *input) {
+extern uint32_t entrypoint(const uint8_t *input) {
   uint64_t x = *(uint64_t *) input;
   uint64_t *result = (uint64_t *) input + 1;
   uint64_t count = 0;
@@ -26,5 +26,5 @@ extern bool entrypoint(const uint8_t *input) {
 
   // sol_log_64(x, count, 0, 0, 0);
   *result = count;
-  return true;
+  return SUCCESS;
 }
diff --git a/programs/bpf/c/src/bench_alu/test_bench_alu.c b/programs/bpf/c/src/bench_alu/test_bench_alu.c
index 87b4ae8b0c..7219d977e8 100644
--- a/programs/bpf/c/src/bench_alu/test_bench_alu.c
+++ b/programs/bpf/c/src/bench_alu/test_bench_alu.c
@@ -4,7 +4,7 @@
 Test(bench_alu, sanity) {
   uint64_t input[] = {500, 0};
 
-  cr_assert(entrypoint((uint8_t *) input));
+  cr_assert_eq(entrypoint((uint8_t *) input), 0);
 
   cr_assert_eq(input[0], 500);
   cr_assert_eq(input[1], 5);
diff --git a/programs/bpf/c/src/bpf_to_bpf/entrypoint.c b/programs/bpf/c/src/bpf_to_bpf/entrypoint.c
index 8689ed3be8..3e55cc137b 100644
--- a/programs/bpf/c/src/bpf_to_bpf/entrypoint.c
+++ b/programs/bpf/c/src/bpf_to_bpf/entrypoint.c
@@ -6,9 +6,9 @@
 
 #include "helper.h"
 
-extern bool entrypoint(const uint8_t *input) {
+extern uint32_t entrypoint(const uint8_t *input) {
   sol_log(__FILE__);
   helper_function();
   sol_log(__FILE__);
-  return true;
+  return SUCCESS;
 }
diff --git a/programs/bpf/c/src/move_funds/move_funds.c b/programs/bpf/c/src/move_funds/move_funds.c
index 8afae5f8d6..4201f770b3 100644
--- a/programs/bpf/c/src/move_funds/move_funds.c
+++ b/programs/bpf/c/src/move_funds/move_funds.c
@@ -11,17 +11,27 @@
  */
 #define NUM_KA 3
 
-extern bool entrypoint(const uint8_t *input) {
+/**
+ * Custom error for when input serialization fails
+ */
+#define INVALID_INPUT 1
+
+/**
+ * Custom error for when transaction is not signed properly
+ */
+#define NOT_SIGNED 2
+
+extern uint32_t entrypoint(const uint8_t *input) {
   SolKeyedAccount ka[NUM_KA];
   SolParameters params = (SolParameters) { .ka = ka };
 
   if (!sol_deserialize(input, &params, SOL_ARRAY_SIZE(ka))) {
-    return false;
+    return INVALID_INPUT;
   }
 
   if (!params.ka[0].is_signer) {
     sol_log("Transaction not signed by key 0");
-    return false;
+    return NOT_SIGNED;
   }
 
   int64_t lamports = *(int64_t *)params.data;
@@ -32,5 +42,5 @@ extern bool entrypoint(const uint8_t *input) {
   } else {
     // sol_log_64(0, 0, 0xFF, *ka[0].lamports, lamports);
   }
-  return true;
+  return SUCCESS;
 }
diff --git a/programs/bpf/c/src/multiple_static/multiple_static.c b/programs/bpf/c/src/multiple_static/multiple_static.c
index 04fd0fd2ee..f838f2b3ac 100644
--- a/programs/bpf/c/src/multiple_static/multiple_static.c
+++ b/programs/bpf/c/src/multiple_static/multiple_static.c
@@ -3,8 +3,8 @@
 static const char msg[] = "This is a message";
 static const char msg2[] = "This is a different message";
 
-extern bool entrypoint(const uint8_t *input) {
+extern uint32_t entrypoint(const uint8_t *input) {
   sol_log((char*)msg);
   sol_log((char*)msg2);
-  return true;
+  return SUCCESS;
 }
diff --git a/programs/bpf/c/src/noop++/noop++.cc b/programs/bpf/c/src/noop++/noop++.cc
index b5dfa8f135..0f62db39da 100644
--- a/programs/bpf/c/src/noop++/noop++.cc
+++ b/programs/bpf/c/src/noop++/noop++.cc
@@ -4,19 +4,24 @@
  */
 #include <solana_sdk.h>
 
-extern bool entrypoint(const uint8_t *input) {
+/**
+ * Custom error for when input serialization fails
+ */
+#define INVALID_INPUT 1
+
+extern uint32_t entrypoint(const uint8_t *input) {
   SolKeyedAccount ka[1];
   SolParameters params = (SolParameters) { .ka = ka };
 
   sol_log(__FILE__);
 
   if (!sol_deserialize(input, &params, SOL_ARRAY_SIZE(ka))) {
-    return false;
+    return INVALID_INPUT;
   }
 
   // Log the provided input parameters.  In the case of  the no-op
   // program, no account keys or input data are expected but real
   // programs will have specific requirements so they can do their work.
   sol_log_params(&params);
-  return true;
+  return SUCCESS;
 }
diff --git a/programs/bpf/c/src/noop/noop.c b/programs/bpf/c/src/noop/noop.c
index 3a158be883..1f03047f1f 100644
--- a/programs/bpf/c/src/noop/noop.c
+++ b/programs/bpf/c/src/noop/noop.c
@@ -4,20 +4,24 @@
  */
 #include <solana_sdk.h>
 
-extern bool entrypoint(const uint8_t *input) {
+/**
+ * Custom error for when input serialization fails
+ */
+#define INVALID_INPUT 1
+
+extern uint32_t entrypoint(const uint8_t *input) {
   SolKeyedAccount ka[1];
   SolParameters params = (SolParameters) { .ka = ka };
 
   sol_log(__FILE__);
 
   if (!sol_deserialize(input, &params, SOL_ARRAY_SIZE(ka))) {
-    return false;
+    return INVALID_INPUT;
   }
 
   // Log the provided input parameters.  In the case of  the no-op
   // program, no account keys or input data are expected but real
   // programs will have specific requirements so they can do their work.
   sol_log_params(&params);
-  return true;
+  return SUCCESS;
 }
-
diff --git a/programs/bpf/c/src/panic/panic.c b/programs/bpf/c/src/panic/panic.c
index c6e773643f..28355737a4 100644
--- a/programs/bpf/c/src/panic/panic.c
+++ b/programs/bpf/c/src/panic/panic.c
@@ -4,8 +4,7 @@
  */
 #include <solana_sdk.h>
 
-extern bool entrypoint(const uint8_t *input) {
+extern uint32_t entrypoint(const uint8_t *input) {
   sol_panic();
-  return true;
+  return SUCCESS;
 }
-
diff --git a/programs/bpf/c/src/relative_call/relative_call.c b/programs/bpf/c/src/relative_call/relative_call.c
index 84627ad5ca..7200987b6c 100644
--- a/programs/bpf/c/src/relative_call/relative_call.c
+++ b/programs/bpf/c/src/relative_call/relative_call.c
@@ -8,9 +8,8 @@ void __attribute__ ((noinline)) helper() {
   sol_log(__func__);
 }
 
-extern bool entrypoint(const uint8_t *input) {
+extern uint32_t entrypoint(const uint8_t *input) {
   sol_log(__func__);
   helper();
-  return true;
+  return SUCCESS;
 }
-
diff --git a/programs/bpf/c/src/struct_pass/struct_pass.c b/programs/bpf/c/src/struct_pass/struct_pass.c
index f401c1a316..165df0bbaf 100644
--- a/programs/bpf/c/src/struct_pass/struct_pass.c
+++ b/programs/bpf/c/src/struct_pass/struct_pass.c
@@ -3,15 +3,14 @@
 struct foo {const uint8_t *input;};
 void foo(const uint8_t *input, struct foo foo) ;
 
-extern bool entrypoint(const uint8_t *input) {
+extern uint32_t entrypoint(const uint8_t *input) {
   struct foo f;
   f.input = input;
   foo(input, f);
-  return true;
+  return SUCCESS;
 }
 
 void foo(const uint8_t *input, struct foo foo) {
   sol_log_64(0, 0, 0, (uint64_t)input, (uint64_t)foo.input);
   sol_assert(input == foo.input);
 }
-
diff --git a/programs/bpf/c/src/struct_ret/struct_ret.c b/programs/bpf/c/src/struct_ret/struct_ret.c
index 7fd87c398d..62ff212f0e 100644
--- a/programs/bpf/c/src/struct_ret/struct_ret.c
+++ b/programs/bpf/c/src/struct_ret/struct_ret.c
@@ -1,5 +1,10 @@
 #include <solana_sdk.h>
 
+/**
+ * Custom error for when struct doesn't add to 12
+ */
+#define INCORRECT_SUM 1
+
 struct test_struct { uint64_t x; uint64_t y; uint64_t z;};
 
 static struct test_struct __attribute__ ((noinline)) test_function(void) {
@@ -10,12 +15,11 @@ static struct test_struct __attribute__ ((noinline)) test_function(void) {
   return s;
 }
 
-extern bool entrypoint(const uint8_t* input) {
+extern uint32_t entrypoint(const uint8_t* input) {
   struct test_struct s = test_function();
   sol_log("foobar");
   if (s.x + s.y + s.z == 12 ) {
-    return true;
+    return SUCCESS;
   }
-  return false;
+  return INCORRECT_SUM;
 }
-
diff --git a/programs/bpf/rust/128bit/src/lib.rs b/programs/bpf/rust/128bit/src/lib.rs
index fe8a06f26f..001ef79dae 100644
--- a/programs/bpf/rust/128bit/src/lib.rs
+++ b/programs/bpf/rust/128bit/src/lib.rs
@@ -1,10 +1,11 @@
 //! @brief Example Rust-based BPF program tests loop iteration
 
 extern crate solana_sdk;
+use solana_sdk::entrypoint::SUCCESS;
 use solana_sdk::info;
 
 #[no_mangle]
-pub extern "C" fn entrypoint(_input: *mut u8) -> bool {
+pub extern "C" fn entrypoint(_input: *mut u8) -> u32 {
     let x: u128 = 1;
     let y = x.rotate_right(1);
     assert_eq!(y, 170_141_183_460_469_231_731_687_303_715_884_105_728);
@@ -48,5 +49,5 @@ pub extern "C" fn entrypoint(_input: *mut u8) -> bool {
     assert_eq!(x, 0x0001_ffff_ffff_ffff_fffe);
 
     info!("Success");
-    true
+    SUCCESS
 }
diff --git a/programs/bpf/rust/alloc/src/lib.rs b/programs/bpf/rust/alloc/src/lib.rs
index 1281fd1472..bc8de66220 100644
--- a/programs/bpf/rust/alloc/src/lib.rs
+++ b/programs/bpf/rust/alloc/src/lib.rs
@@ -3,12 +3,13 @@
 #[macro_use]
 extern crate alloc;
 extern crate solana_sdk;
+use solana_sdk::entrypoint::SUCCESS;
 use solana_sdk::info;
 use std::alloc::Layout;
 use std::mem;
 
 #[no_mangle]
-pub extern "C" fn entrypoint(_input: *mut u8) -> bool {
+pub extern "C" fn entrypoint(_input: *mut u8) -> u32 {
     unsafe {
         // Confirm large allocation fails
 
@@ -100,5 +101,5 @@ pub extern "C" fn entrypoint(_input: *mut u8) -> bool {
     }
 
     info!("Success");
-    true
+    SUCCESS
 }
diff --git a/programs/bpf/rust/dep_crate/src/lib.rs b/programs/bpf/rust/dep_crate/src/lib.rs
index 3a74dccef3..f8f3968163 100644
--- a/programs/bpf/rust/dep_crate/src/lib.rs
+++ b/programs/bpf/rust/dep_crate/src/lib.rs
@@ -2,10 +2,11 @@
 
 extern crate solana_sdk;
 use byteorder::{ByteOrder, LittleEndian};
+use solana_sdk::entrypoint::SUCCESS;
 use solana_sdk::info;
 
 #[no_mangle]
-pub extern "C" fn entrypoint(_input: *mut u8) -> bool {
+pub extern "C" fn entrypoint(_input: *mut u8) -> u32 {
     let mut buf = [0; 4];
     LittleEndian::write_u32(&mut buf, 1_000_000);
     assert_eq!(1_000_000, LittleEndian::read_u32(&buf));
@@ -15,5 +16,5 @@ pub extern "C" fn entrypoint(_input: *mut u8) -> bool {
     assert_eq!(-5_000, LittleEndian::read_i16(&buf));
 
     info!("Success");
-    true
+    SUCCESS
 }
diff --git a/programs/bpf/rust/external_spend/src/lib.rs b/programs/bpf/rust/external_spend/src/lib.rs
index a50ecca439..1d3cde76d3 100644
--- a/programs/bpf/rust/external_spend/src/lib.rs
+++ b/programs/bpf/rust/external_spend/src/lib.rs
@@ -6,11 +6,10 @@ use solana_sdk::entrypoint::*;
 use solana_sdk::pubkey::Pubkey;
 
 entrypoint!(process_instruction);
-fn process_instruction(_program_id: &Pubkey, ka: &mut [SolKeyedAccount], _data: &[u8]) -> bool {
+fn process_instruction(_program_id: &Pubkey, ka: &mut [SolKeyedAccount], _data: &[u8]) -> u32 {
     // account 0 is the mint and not owned by this program, any debit of its lamports
     // should result in a failed program execution.  Test to ensure that this debit
     // is seen by the runtime and fails as expected
     *ka[0].lamports -= 1;
-
-    true
+    SUCCESS
 }
diff --git a/programs/bpf/rust/iter/src/lib.rs b/programs/bpf/rust/iter/src/lib.rs
index 8bd046fb90..7361817cff 100644
--- a/programs/bpf/rust/iter/src/lib.rs
+++ b/programs/bpf/rust/iter/src/lib.rs
@@ -1,10 +1,11 @@
 //! @brief Example Rust-based BPF program tests loop iteration
 
 extern crate solana_sdk;
+use solana_sdk::entrypoint::SUCCESS;
 use solana_sdk::info;
 
 #[no_mangle]
-pub extern "C" fn entrypoint(_input: *mut u8) -> bool {
+pub extern "C" fn entrypoint(_input: *mut u8) -> u32 {
     const ITERS: usize = 100;
     let ones = [1_u64; ITERS];
     let mut sum: u64 = 0;
@@ -16,5 +17,5 @@ pub extern "C" fn entrypoint(_input: *mut u8) -> bool {
     assert_eq!(sum, ITERS as u64);
 
     info!("Success");
-    true
+    SUCCESS
 }
diff --git a/programs/bpf/rust/many_args/src/lib.rs b/programs/bpf/rust/many_args/src/lib.rs
index 6cee830644..fef3441625 100644
--- a/programs/bpf/rust/many_args/src/lib.rs
+++ b/programs/bpf/rust/many_args/src/lib.rs
@@ -2,10 +2,11 @@
 
 mod helper;
 extern crate solana_sdk;
+use solana_sdk::entrypoint::SUCCESS;
 use solana_sdk::info;
 
 #[no_mangle]
-pub extern "C" fn entrypoint(_input: *mut u8) -> bool {
+pub extern "C" fn entrypoint(_input: *mut u8) -> u32 {
     info!("Call same package");
     assert_eq!(crate::helper::many_args(1, 2, 3, 4, 5, 6, 7, 8, 9), 45);
 
@@ -24,5 +25,5 @@ pub extern "C" fn entrypoint(_input: *mut u8) -> bool {
     );
 
     info!("Success");
-    true
+    SUCCESS
 }
diff --git a/programs/bpf/rust/noop/src/lib.rs b/programs/bpf/rust/noop/src/lib.rs
index 1b31b415b7..a9e1918d5a 100644
--- a/programs/bpf/rust/noop/src/lib.rs
+++ b/programs/bpf/rust/noop/src/lib.rs
@@ -21,7 +21,7 @@ fn return_sstruct() -> SStruct {
 }
 
 entrypoint!(process_instruction);
-fn process_instruction(program_id: &Pubkey, ka: &mut [SolKeyedAccount], data: &[u8]) -> bool {
+fn process_instruction(program_id: &Pubkey, ka: &mut [SolKeyedAccount], data: &[u8]) -> u32 {
     info!("Program identifier:");
     program_id.log();
 
@@ -56,7 +56,7 @@ fn process_instruction(program_id: &Pubkey, ka: &mut [SolKeyedAccount], data: &[
     }
 
     info!("Success");
-    true
+    SUCCESS
 }
 
 #[cfg(test)]
diff --git a/programs/bpf/rust/panic/src/lib.rs b/programs/bpf/rust/panic/src/lib.rs
index c862901568..4b5463591b 100644
--- a/programs/bpf/rust/panic/src/lib.rs
+++ b/programs/bpf/rust/panic/src/lib.rs
@@ -3,6 +3,6 @@
 extern crate solana_sdk;
 
 #[no_mangle]
-pub extern "C" fn entrypoint(_input: *mut u8) -> bool {
+pub extern "C" fn entrypoint(_input: *mut u8) -> u32 {
     panic!();
 }
diff --git a/programs/bpf/rust/param_passing/src/lib.rs b/programs/bpf/rust/param_passing/src/lib.rs
index d2e737662f..1170fac991 100644
--- a/programs/bpf/rust/param_passing/src/lib.rs
+++ b/programs/bpf/rust/param_passing/src/lib.rs
@@ -2,10 +2,11 @@
 
 extern crate solana_sdk;
 use solana_bpf_rust_param_passing_dep::{Data, TestDep};
+use solana_sdk::entrypoint::SUCCESS;
 use solana_sdk::info;
 
 #[no_mangle]
-pub extern "C" fn entrypoint(_input: *mut u8) -> bool {
+pub extern "C" fn entrypoint(_input: *mut u8) -> u32 {
     let array = [0xA, 0xB, 0xC, 0xD, 0xE, 0xF];
     let data = Data {
         twentyone: 21u64,
@@ -18,5 +19,6 @@ pub extern "C" fn entrypoint(_input: *mut u8) -> bool {
 
     let test_dep = TestDep::new(&data, 1, 2, 3, 4, 5);
     info!(0, 0, 0, 0, test_dep.thirty);
-    test_dep.thirty == 30
+    assert!(test_dep.thirty == 30);
+    SUCCESS
 }
diff --git a/programs/bpf/rust/tick_height/src/lib.rs b/programs/bpf/rust/tick_height/src/lib.rs
index 888f67f7ea..39a759a467 100644
--- a/programs/bpf/rust/tick_height/src/lib.rs
+++ b/programs/bpf/rust/tick_height/src/lib.rs
@@ -7,10 +7,10 @@ use solana_sdk::pubkey::Pubkey;
 use solana_sdk::{entrypoint, info};
 
 entrypoint!(process_instruction);
-fn process_instruction(_program_id: &Pubkey, ka: &mut [SolKeyedAccount], _data: &[u8]) -> bool {
+fn process_instruction(_program_id: &Pubkey, ka: &mut [SolKeyedAccount], _data: &[u8]) -> u32 {
     let tick_height = LittleEndian::read_u64(ka[2].data);
     assert_eq!(10u64, tick_height);
 
     info!("Success");
-    true
+    SUCCESS
 }
diff --git a/programs/bpf_loader_api/src/lib.rs b/programs/bpf_loader_api/src/lib.rs
index 7882b557f4..d119123324 100644
--- a/programs/bpf_loader_api/src/lib.rs
+++ b/programs/bpf_loader_api/src/lib.rs
@@ -20,6 +20,7 @@ use solana_sdk::account::KeyedAccount;
 use solana_sdk::instruction::InstructionError;
 use solana_sdk::loader_instruction::LoaderInstruction;
 use solana_sdk::pubkey::Pubkey;
+use std::convert::TryFrom;
 use std::io::prelude::*;
 use std::io::Error;
 use std::mem;
@@ -136,12 +137,18 @@ pub fn process_instruction(
                 let mut v = serialize_parameters(program_id, params, &data);
 
                 match vm.execute_program(v.as_mut_slice(), &[], &[heap_region]) {
-                    Ok(status) => {
-                        if 0 == status {
-                            warn!("BPF program failed: {}", status);
+                    Ok(status) => match u32::try_from(status) {
+                        Ok(status) => {
+                            if status > 0 {
+                                warn!("BPF program failed: {}", status);
+                                return Err(InstructionError::CustomError(status));
+                            }
+                        }
+                        Err(e) => {
+                            warn!("BPF VM encountered invalid status: {}", e);
                             return Err(InstructionError::GenericError);
                         }
-                    }
+                    },
                     Err(e) => {
                         warn!("BPF VM failed to run program: {}", e);
                         return Err(InstructionError::GenericError);
diff --git a/sdk/bpf/c/inc/solana_sdk.h b/sdk/bpf/c/inc/solana_sdk.h
index d61e8a344d..fadf26aba5 100644
--- a/sdk/bpf/c/inc/solana_sdk.h
+++ b/sdk/bpf/c/inc/solana_sdk.h
@@ -51,6 +51,11 @@ static_assert(sizeof(uint64_t) == 8);
  */
 #define NULL 0
 
+/**
+ * SUCCESS return value
+ */
+#define SUCCESS 0
+
 /**
  * Boolean type
  */
@@ -319,9 +324,9 @@ SOL_FN_PREFIX void sol_log_params(const SolParameters *params) {
  * Program instruction entrypoint
  *
  * @param input Buffer of serialized input parameters.  Use sol_deserialize() to decode
- * @return true if the instruction executed successfully
+ * @return 0 if the instruction executed successfully
  */
-bool entrypoint(const uint8_t *input);
+uint32_t entrypoint(const uint8_t *input);
 
 
 #ifdef SOL_TEST
diff --git a/sdk/src/entrypoint.rs b/sdk/src/entrypoint.rs
index 2deb049272..2bc6917b55 100644
--- a/sdk/src/entrypoint.rs
+++ b/sdk/src/entrypoint.rs
@@ -28,6 +28,9 @@ pub struct SolKeyedAccount<'a> {
 pub type ProcessInstruction =
     fn(program_id: &Pubkey, accounts: &mut [SolKeyedAccount], data: &[u8]) -> bool;
 
+/// Programs indicate success with a return value of 0
+pub const SUCCESS: u32 = 0;
+
 /// Declare entrypoint of the program.
 ///
 /// Deserialize the program input parameters and call
@@ -38,13 +41,10 @@ pub type ProcessInstruction =
 macro_rules! entrypoint {
     ($process_instruction:ident) => {
         #[no_mangle]
-        pub unsafe extern "C" fn entrypoint(input: *mut u8) -> bool {
+        pub unsafe extern "C" fn entrypoint(input: *mut u8) -> u32 {
                unsafe {
-                if let Ok((program_id, mut kas, data)) = $crate::entrypoint::deserialize(input) {
-                    $process_instruction(&program_id, &mut kas, &data)
-                } else {
-                    false
-                }
+                let (program_id, mut kas, data) = $crate::entrypoint::deserialize(input);
+                $process_instruction(&program_id, &mut kas, &data)
             }
         }
     };
@@ -54,7 +54,7 @@ macro_rules! entrypoint {
 #[allow(clippy::type_complexity)]
 pub unsafe fn deserialize<'a>(
     input: *mut u8,
-) -> Result<(&'a Pubkey, Vec<SolKeyedAccount<'a>>, &'a [u8]), ()> {
+) -> (&'a Pubkey, Vec<SolKeyedAccount<'a>>, &'a [u8]) {
     let mut offset: usize = 0;
 
     // Number of KeyedAccounts present
@@ -113,5 +113,5 @@ pub unsafe fn deserialize<'a>(
 
     let program_id: &Pubkey = &*(input.add(offset) as *const Pubkey);
 
-    Ok((program_id, kas, data))
+    (program_id, kas, data)
 }
diff --git a/sdk/src/instruction.rs b/sdk/src/instruction.rs
index 7e7f9fa79b..026c89d606 100644
--- a/sdk/src/instruction.rs
+++ b/sdk/src/instruction.rs
@@ -70,6 +70,9 @@ pub enum InstructionError {
     /// 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.
+    ///
+    /// NOTE: u64 requires special serialization to avoid the loss of precision in JS clients and
+    /// so is not used for now.
     CustomError(u32),
 }