diff --git a/miner/src/transaction_queue.rs b/miner/src/transaction_queue.rs
index ecfb2b8b0..6a1721f1d 100644
--- a/miner/src/transaction_queue.rs
+++ b/miner/src/transaction_queue.rs
@@ -672,10 +672,10 @@ impl TransactionQueue {
 }
 
 fn check_too_cheap(is_in: bool) -> Result<(), TransactionError> {
-	if !is_in {
-		Err(TransactionError::TooCheapToReplace)
-	} else {
+	if is_in {
 		Ok(())
+	} else {
+		Err(TransactionError::TooCheapToReplace)
 	}
 }
 
diff --git a/rpc/src/v1/impls/ethcore.rs b/rpc/src/v1/impls/ethcore.rs
index f15d0a3d5..36116cfaa 100644
--- a/rpc/src/v1/impls/ethcore.rs
+++ b/rpc/src/v1/impls/ethcore.rs
@@ -84,7 +84,7 @@ impl<M> Ethcore for EthcoreClient<M> where M: MinerService + 'static {
 
 	fn dev_logs(&self, _params: Params) -> Result<Value, Error> {
 		let logs = self.logger.logs();
-		to_value(&logs.deref())
+		to_value(&logs.deref().as_slice())
 	}
 
 	fn dev_logs_levels(&self, _params: Params) -> Result<Value, Error> {
diff --git a/rpc/src/v1/tests/ethcore.rs b/rpc/src/v1/tests/ethcore.rs
index 06d4ffc1c..51542e9dc 100644
--- a/rpc/src/v1/tests/ethcore.rs
+++ b/rpc/src/v1/tests/ethcore.rs
@@ -22,16 +22,20 @@ use ethminer::MinerService;
 use v1::tests::helpers::TestMinerService;
 use util::numbers::*;
 use rustc_serialize::hex::FromHex;
+use util::log::RotatingLogger;
 
 
 fn miner_service() -> Arc<TestMinerService> {
 	Arc::new(TestMinerService::default())
 }
+fn logger() -> Arc<RotatingLogger> {
+	Arc::new(RotatingLogger::new("rpc=trace".to_owned()))
+}
 
 #[test]
 fn rpc_ethcore_extra_data() {
 	let miner = miner_service();
-	let ethcore = EthcoreClient::new(&miner).to_delegate();
+	let ethcore = EthcoreClient::new(&miner, logger()).to_delegate();
 	let io = IoHandler::new();
 	io.add_delegate(ethcore);
 
@@ -45,7 +49,7 @@ fn rpc_ethcore_extra_data() {
 #[test]
 fn rpc_ethcore_gas_floor_target() {
 	let miner = miner_service();
-	let ethcore = EthcoreClient::new(&miner).to_delegate();
+	let ethcore = EthcoreClient::new(&miner, logger()).to_delegate();
 	let io = IoHandler::new();
 	io.add_delegate(ethcore);
 
@@ -58,7 +62,7 @@ fn rpc_ethcore_gas_floor_target() {
 #[test]
 fn rpc_ethcore_min_gas_price() {
 	let miner = miner_service();
-	let ethcore = EthcoreClient::new(&miner).to_delegate();
+	let ethcore = EthcoreClient::new(&miner, logger()).to_delegate();
 	let io = IoHandler::new();
 	io.add_delegate(ethcore);
 
@@ -71,7 +75,7 @@ fn rpc_ethcore_min_gas_price() {
 #[test]
 fn rpc_ethcore_set_min_gas_price() {
 	let miner = miner_service();
-	let ethcore = EthcoreClient::new(&miner).to_delegate();
+	let ethcore = EthcoreClient::new(&miner, logger()).to_delegate();
 	let io = IoHandler::new();
 	io.add_delegate(ethcore);
 
@@ -85,7 +89,7 @@ fn rpc_ethcore_set_min_gas_price() {
 #[test]
 fn rpc_ethcore_set_gas_floor_target() {
 	let miner = miner_service();
-	let ethcore = EthcoreClient::new(&miner).to_delegate();
+	let ethcore = EthcoreClient::new(&miner, logger()).to_delegate();
 	let io = IoHandler::new();
 	io.add_delegate(ethcore);
 
@@ -99,7 +103,7 @@ fn rpc_ethcore_set_gas_floor_target() {
 #[test]
 fn rpc_ethcore_set_extra_data() {
 	let miner = miner_service();
-	let ethcore = EthcoreClient::new(&miner).to_delegate();
+	let ethcore = EthcoreClient::new(&miner, logger()).to_delegate();
 	let io = IoHandler::new();
 	io.add_delegate(ethcore);
 
@@ -113,7 +117,7 @@ fn rpc_ethcore_set_extra_data() {
 #[test]
 fn rpc_ethcore_set_author() {
 	let miner = miner_service();
-	let ethcore = EthcoreClient::new(&miner).to_delegate();
+	let ethcore = EthcoreClient::new(&miner, logger()).to_delegate();
 	let io = IoHandler::new();
 	io.add_delegate(ethcore);
 
@@ -123,3 +127,32 @@ fn rpc_ethcore_set_author() {
 	assert_eq!(io.handle_request(request), Some(response.to_owned()));
 	assert_eq!(miner.author(), Address::from_str("cd1722f3947def4cf144679da39c4c32bdc35681").unwrap());
 }
+
+#[test]
+fn rpc_ethcore_dev_logs() {
+	let miner = miner_service();
+	let logger = logger();
+	logger.append("a".to_owned());
+	logger.append("b".to_owned());
+	let ethcore = EthcoreClient::new(&miner, logger.clone()).to_delegate();
+	let io = IoHandler::new();
+	io.add_delegate(ethcore);
+
+	let request = r#"{"jsonrpc": "2.0", "method": "ethcore_devLogs", "params":[], "id": 1}"#;
+	let response = r#"{"jsonrpc":"2.0","result":["b","a"],"id":1}"#;
+
+	assert_eq!(io.handle_request(request), Some(response.to_owned()));
+}
+
+#[test]
+fn rpc_ethcore_dev_logs_levels() {
+	let miner = miner_service();
+	let ethcore = EthcoreClient::new(&miner, logger()).to_delegate();
+	let io = IoHandler::new();
+	io.add_delegate(ethcore);
+
+	let request = r#"{"jsonrpc": "2.0", "method": "ethcore_devLogsLevels", "params":[], "id": 1}"#;
+	let response = r#"{"jsonrpc":"2.0","result":"rpc=trace","id":1}"#;
+
+	assert_eq!(io.handle_request(request), Some(response.to_owned()));
+}
diff --git a/util/src/log.rs b/util/src/log.rs
index c5ad40239..45017bfcd 100644
--- a/util/src/log.rs
+++ b/util/src/log.rs
@@ -20,7 +20,7 @@ use std::env;
 use rlog::{LogLevelFilter};
 use env_logger::LogBuilder;
 use std::sync::{RwLock, RwLockReadGuard};
-use std::sync::atomic::{AtomicBool, AtomicUsize, Ordering};
+use arrayvec::ArrayVec;
 
 lazy_static! {
 	static ref LOG_DUMMY: bool = {
@@ -43,35 +43,39 @@ pub fn init_log() {
 	let _ = *LOG_DUMMY;
 }
 
-static LOG_SIZE : usize = 128;
+const LOG_SIZE : usize = 128;
 
+/// Logger implementation that keeps up to `LOG_SIZE` log elements.
 pub struct RotatingLogger {
-	idx: AtomicUsize,
+	/// Defined logger levels
 	levels: String,
-	logs: RwLock<Vec<String>>,
+	/// Logs array. Latest log is always at index 0
+	logs: RwLock<ArrayVec<[String; LOG_SIZE]>>,
 }
 
 impl RotatingLogger {
 
+	/// Creates new `RotatingLogger` with given levels.
+	/// It does not enforce levels - it's just read only.
 	pub fn new(levels: String) -> Self {
 		RotatingLogger {
-			idx: AtomicUsize::new(0),
 			levels: levels,
-			logs: RwLock::new(Vec::with_capacity(LOG_SIZE)),
+			logs: RwLock::new(ArrayVec::<[_; LOG_SIZE]>::new()),
 		}
 	}
 
+	/// Append new log entry
 	pub fn append(&self, log: String) {
-		let idx = self.idx.fetch_add(1, Ordering::SeqCst);
-		let idx = idx % LOG_SIZE;
-		self.logs.write().unwrap().insert(idx, log);
+		self.logs.write().unwrap().insert(0, log);
 	}
 
+	/// Return levels
 	pub fn levels(&self) -> &str {
 		&self.levels
 	}
 
-	pub fn logs(&self) -> RwLockReadGuard<Vec<String>> {
+	/// Return logs
+	pub fn logs(&self) -> RwLockReadGuard<ArrayVec<[String; LOG_SIZE]>> {
 		self.logs.read().unwrap()
 	}