diff --git a/sync/src/light_sync/mod.rs b/sync/src/light_sync/mod.rs
index 12db882f0..ef1bd8742 100644
--- a/sync/src/light_sync/mod.rs
+++ b/sync/src/light_sync/mod.rs
@@ -35,6 +35,7 @@
 use std::collections::{HashMap, HashSet};
 use std::mem;
 use std::sync::Arc;
+use std::time::{Instant, Duration};
 
 use ethcore::encoded;
 use light::client::{AsLightClient, LightChainClient};
@@ -57,6 +58,13 @@ mod sync_round;
 #[cfg(test)]
 mod tests;
 
+// Base number of milliseconds for the header request timeout.
+const REQ_TIMEOUT_MILLISECS_BASE: u64 = 7000;
+// Additional number of milliseconds for each requested header.
+// If we request N headers, then the timeout will be:
+//  REQ_TIMEOUT_MILLISECS_BASE + N * REQ_TIMEOUT_MILLISECS_PER_HEADER
+const REQ_TIMEOUT_MILLISECS_PER_HEADER: u64 = 10;
+
 /// Peer chain info.
 #[derive(Debug, Clone, PartialEq, Eq)]
 struct ChainInfo {
@@ -224,12 +232,18 @@ pub struct LightSync<L: AsLightClient> {
 	start_block_number: u64,
 	best_seen: Mutex<Option<ChainInfo>>, // best seen block on the network.
 	peers: RwLock<HashMap<PeerId, Mutex<Peer>>>, // peers which are relevant to synchronization.
-	pending_reqs: Mutex<HashSet<ReqId>>, // requests from this handler.
+	pending_reqs: Mutex<HashMap<ReqId, PendingReq>>, // requests from this handler
 	client: Arc<L>,
 	rng: Mutex<OsRng>,
 	state: Mutex<SyncState>,
 }
 
+#[derive(Debug, Clone)]
+struct PendingReq {
+	started: Instant,
+	timeout: Duration,
+}
+
 impl<L: AsLightClient + Send + Sync> Handler for LightSync<L> {
 	fn on_connect(
 		&self,
@@ -352,7 +366,7 @@ impl<L: AsLightClient + Send + Sync> Handler for LightSync<L> {
 			return
 		}
 
-		if !self.pending_reqs.lock().remove(&req_id) {
+		if self.pending_reqs.lock().remove(&req_id).is_none() {
 			return
 		}
 
@@ -411,7 +425,7 @@ impl<L: AsLightClient> LightSync<L> {
 		*state = SyncState::AncestorSearch(AncestorSearch::begin(chain_info.best_block_number));
 	}
 
-	// handles request dispatch, block import, and state machine transitions.
+	// handles request dispatch, block import, state machine transitions, and timeouts.
 	fn maintain_sync(&self, ctx: &BasicContext) {
 		const DRAIN_AMOUNT: usize = 128;
 
@@ -501,6 +515,32 @@ impl<L: AsLightClient> LightSync<L> {
 			}
 		}
 
+		// handle requests timeouts
+		{
+			let mut pending_reqs = self.pending_reqs.lock();
+			let mut unfulfilled = Vec::new();
+			for (req_id, info) in pending_reqs.iter() {
+				if info.started.elapsed() >= info.timeout {
+					debug!(target: "sync", "{} timed out", req_id);
+					unfulfilled.push(req_id.clone());
+				}
+			}
+
+			if !unfulfilled.is_empty() {
+				for unfulfilled in unfulfilled.iter() {
+					pending_reqs.remove(unfulfilled);
+				}
+				drop(pending_reqs);
+
+				*state = match mem::replace(&mut *state, SyncState::Idle) {
+					SyncState::Idle => SyncState::Idle,
+					SyncState::AncestorSearch(search) =>
+						SyncState::AncestorSearch(search.requests_abandoned(&unfulfilled)),
+					SyncState::Rounds(round) => SyncState::Rounds(round.requests_abandoned(&unfulfilled)),
+				};
+			}
+		}
+
 		// allow dispatching of requests.
 		{
 			let peers = self.peers.read();
@@ -534,7 +574,12 @@ impl<L: AsLightClient> LightSync<L> {
 					if requested_from.contains(peer) { continue }
 					match ctx.request_from(*peer, request.clone()) {
 						Ok(id) => {
-							self.pending_reqs.lock().insert(id.clone());
+							let timeout_ms = REQ_TIMEOUT_MILLISECS_BASE +
+								req.max * REQ_TIMEOUT_MILLISECS_PER_HEADER;
+							self.pending_reqs.lock().insert(id.clone(), PendingReq {
+								started: Instant::now(),
+								timeout: Duration::from_millis(timeout_ms),
+							});
 							requested_from.insert(peer.clone());
 
 							return Some(id)
@@ -570,7 +615,7 @@ impl<L: AsLightClient> LightSync<L> {
 			start_block_number: client.as_light_client().chain_info().best_block_number,
 			best_seen: Mutex::new(None),
 			peers: RwLock::new(HashMap::new()),
-			pending_reqs: Mutex::new(HashSet::new()),
+			pending_reqs: Mutex::new(HashMap::new()),
 			client: client,
 			rng: Mutex::new(OsRng::new()?),
 			state: Mutex::new(SyncState::Idle),
diff --git a/sync/src/light_sync/sync_round.rs b/sync/src/light_sync/sync_round.rs
index 4fa7a528b..d477ecc81 100644
--- a/sync/src/light_sync/sync_round.rs
+++ b/sync/src/light_sync/sync_round.rs
@@ -179,7 +179,7 @@ impl Fetcher {
 		};
 
 		trace!(target: "sync", "Received response for subchain ({} -> {})",
-			request.subchain_parent.0 + 1, request.subchain_end.0);
+			request.subchain_parent.0, request.subchain_end.0);
 
 		let headers = ctx.data();
 
@@ -241,6 +241,8 @@ impl Fetcher {
 	}
 
 	fn requests_abandoned(mut self, abandoned: &[ReqId]) -> SyncRound {
+		trace!(target: "sync", "Abandonned requests {:?}", abandoned);
+
 		for abandoned in abandoned {
 			match self.pending.remove(abandoned) {
 				None => {},
@@ -258,12 +260,14 @@ impl Fetcher {
 		while let Some(pending_req) = self.requests.pop() {
 			match dispatcher(pending_req.headers_request.clone()) {
 				Some(req_id) => {
-					trace!(target: "sync", "Assigned request for subchain ({} -> {})",
-						pending_req.subchain_parent.0 + 1, pending_req.subchain_end.0);
+					trace!(target: "sync", "Assigned request {} for subchain ({} -> {})",
+						req_id, pending_req.subchain_parent.0, pending_req.subchain_end.0);
 
 					self.pending.insert(req_id, pending_req);
 				}
 				None => {
+					trace!(target: "sync", "Failed to assign request for subchain ({} -> {})",
+						pending_req.subchain_parent.0, pending_req.subchain_end.0);
 					self.requests.push(pending_req);
 					break;
 				}