diff --git a/ethcore/src/executive.rs b/ethcore/src/executive.rs
index b0b0b58c856..97bbafed804 100644
--- a/ethcore/src/executive.rs
+++ b/ethcore/src/executive.rs
@@ -25,10 +25,10 @@ use trace::{FlatTrace, Tracer, NoopTracer, ExecutiveTracer, VMTrace, VMTracer, E
 use crossbeam;
 pub use types::executed::{Executed, ExecutionResult};
 
-/// Max depth to avoid stack overflow (when it's reached we start a new thread with VM)
+/// Roughly estimate what stack size each level of evm depth will use
 /// TODO [todr] We probably need some more sophisticated calculations here (limit on my machine 132)
 /// Maybe something like here: `https://github.com/ethereum/libethereum/blob/4db169b8504f2b87f7d5a481819cfb959fc65f6c/libethereum/ExtVM.cpp`
-const MAX_VM_DEPTH_FOR_THREAD: usize = 64;
+const STACK_SIZE_PER_DEPTH: usize = 24*1024;
 
 /// Returns new address created from address and given nonce.
 pub fn contract_address(address: &Address, nonce: &U256) -> Address {
@@ -149,12 +149,13 @@ impl<'a> Executive<'a> {
 
 		// TODO: we might need bigints here, or at least check overflows.
 		let balance = self.state.balance(&sender);
-		let gas_cost = U512::from(t.gas) * U512::from(t.gas_price);
+		let gas_cost = t.gas.full_mul(t.gas_price);
 		let total_cost = U512::from(t.value) + gas_cost;
 
 		// avoid unaffordable transactions
-		if U512::from(balance) < total_cost {
-			return Err(From::from(ExecutionError::NotEnoughCash { required: total_cost, got: U512::from(balance) }));
+		let balance512 = U512::from(balance);
+		if balance512 < total_cost {
+			return Err(From::from(ExecutionError::NotEnoughCash { required: total_cost, got: balance512 }));
 		}
 
 		// NOTE: there can be no invalid transactions from this point.
@@ -212,8 +213,11 @@ impl<'a> Executive<'a> {
 		tracer: &mut T,
 		vm_tracer: &mut V
 	) -> evm::Result<U256> where T: Tracer, V: VMTracer {
+
+		let depth_threshold = ::io::LOCAL_STACK_SIZE.with(|sz| sz.get() / STACK_SIZE_PER_DEPTH);
+
 		// Ordinary execution - keep VM in same thread
-		if (self.depth + 1) % MAX_VM_DEPTH_FOR_THREAD != 0 {
+		if (self.depth + 1) % depth_threshold != 0 {
 			let vm_factory = self.vm_factory;
 			let mut ext = self.as_externalities(OriginInfo::from(&params), unconfirmed_substate, output_policy, tracer, vm_tracer);
 			trace!(target: "executive", "ext.schedule.have_delegate_call: {}", ext.schedule().have_delegate_call);
@@ -413,7 +417,7 @@ impl<'a> Executive<'a> {
 
 		// real ammount to refund
 		let gas_left_prerefund = match result { Ok(x) => x, _ => 0.into() };
-		let refunded = cmp::min(refunds_bound, (t.gas - gas_left_prerefund) / U256::from(2));
+		let refunded = cmp::min(refunds_bound, (t.gas - gas_left_prerefund) >> 1);
 		let gas_left = gas_left_prerefund + refunded;
 
 		let gas_used = t.gas - gas_left;
diff --git a/util/io/src/lib.rs b/util/io/src/lib.rs
index b2a16e19bb2..082192dfaf0 100644
--- a/util/io/src/lib.rs
+++ b/util/io/src/lib.rs
@@ -68,6 +68,8 @@ mod panics;
 use mio::{EventLoop, Token};
 use std::fmt;
 
+pub use worker::LOCAL_STACK_SIZE;
+
 #[derive(Debug)]
 /// IO Error
 pub enum IoError {
diff --git a/util/io/src/worker.rs b/util/io/src/worker.rs
index 0176c467cad..f4f63919f14 100644
--- a/util/io/src/worker.rs
+++ b/util/io/src/worker.rs
@@ -22,9 +22,19 @@ use crossbeam::sync::chase_lev;
 use service::{HandlerId, IoChannel, IoContext};
 use IoHandler;
 use panics::*;
+use std::cell::Cell;
 
 use std::sync::{Condvar as SCondvar, Mutex as SMutex};
 
+const STACK_SIZE: usize = 16*1024*1024;
+
+thread_local! {
+	/// Stack size
+	/// Should be modified if it is changed in Rust since it is no way
+	/// to know or get it
+	pub static LOCAL_STACK_SIZE: Cell<usize> = Cell::new(::std::env::var("RUST_MIN_STACK").ok().and_then(|s| s.parse().ok()).unwrap_or(2 * 1024 * 1024));
+}
+
 pub enum WorkType<Message> {
 	Readable,
 	Writable,
@@ -66,8 +76,9 @@ impl Worker {
 			deleting: deleting.clone(),
 			wait_mutex: wait_mutex.clone(),
 		};
-		worker.thread = Some(thread::Builder::new().name(format!("IO Worker #{}", index)).spawn(
+		worker.thread = Some(thread::Builder::new().stack_size(STACK_SIZE).name(format!("IO Worker #{}", index)).spawn(
 			move || {
+				LOCAL_STACK_SIZE.with(|val| val.set(STACK_SIZE));
 				panic_handler.catch_panic(move || {
 					Worker::work_loop(stealer, channel.clone(), wait, wait_mutex.clone(), deleting)
 				}).unwrap()