diff --git a/Cargo.lock b/Cargo.lock
index f340ec6d0a60..55ddaa6b1a29 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -6823,6 +6823,7 @@ dependencies = [
  "polkadot-overseer",
  "polkadot-primitives",
  "polkadot-primitives-test-helpers",
+ "sp-consensus",
  "sp-core",
  "sp-keyring",
  "thiserror",
diff --git a/node/core/av-store/Cargo.toml b/node/core/av-store/Cargo.toml
index ee6bfd7359b8..2f1637cd6ec3 100644
--- a/node/core/av-store/Cargo.toml
+++ b/node/core/av-store/Cargo.toml
@@ -19,6 +19,7 @@ polkadot-node-subsystem-util = { path = "../../subsystem-util" }
 polkadot-overseer = { path = "../../overseer" }
 polkadot-primitives = { path = "../../../primitives" }
 polkadot-node-primitives = { path = "../../primitives" }
+sp-consensus = { git = "https://github.com/paritytech/substrate", branch = "master", default-features = false }
 
 [dev-dependencies]
 log = "0.4.17"
diff --git a/node/core/av-store/src/lib.rs b/node/core/av-store/src/lib.rs
index 4509c5712188..d43dc0657d18 100644
--- a/node/core/av-store/src/lib.rs
+++ b/node/core/av-store/src/lib.rs
@@ -30,6 +30,7 @@ use futures::{channel::oneshot, future, select, FutureExt};
 use futures_timer::Delay;
 use parity_scale_codec::{Decode, Encode, Error as CodecError, Input};
 use polkadot_node_subsystem_util::database::{DBTransaction, Database};
+use sp_consensus::SyncOracle;
 
 use bitvec::{order::Lsb0 as BitOrderLsb0, vec::BitVec};
 use polkadot_node_primitives::{AvailableData, ErasureChunk};
@@ -451,16 +452,23 @@ pub struct AvailabilityStoreSubsystem {
 	finalized_number: Option<BlockNumber>,
 	metrics: Metrics,
 	clock: Box<dyn Clock>,
+	sync_oracle: Box<dyn SyncOracle + Send + Sync>,
 }
 
 impl AvailabilityStoreSubsystem {
 	/// Create a new `AvailabilityStoreSubsystem` with a given config on disk.
-	pub fn new(db: Arc<dyn Database>, config: Config, metrics: Metrics) -> Self {
+	pub fn new(
+		db: Arc<dyn Database>,
+		config: Config,
+		sync_oracle: Box<dyn SyncOracle + Send + Sync>,
+		metrics: Metrics,
+	) -> Self {
 		Self::with_pruning_config_and_clock(
 			db,
 			config,
 			PruningConfig::default(),
 			Box::new(SystemClock),
+			sync_oracle,
 			metrics,
 		)
 	}
@@ -471,6 +479,7 @@ impl AvailabilityStoreSubsystem {
 		config: Config,
 		pruning_config: PruningConfig,
 		clock: Box<dyn Clock>,
+		sync_oracle: Box<dyn SyncOracle + Send + Sync>,
 		metrics: Metrics,
 	) -> Self {
 		Self {
@@ -480,6 +489,7 @@ impl AvailabilityStoreSubsystem {
 			metrics,
 			clock,
 			known_blocks: KnownUnfinalizedBlocks::default(),
+			sync_oracle,
 			finalized_number: None,
 		}
 	}
@@ -576,7 +586,12 @@ async fn run_iteration<Context>(
 						// candidates backed in this finalized block.
 						// Otherwise, we won't be able to store our chunk
 						// for these candidates.
-						process_block_activated(ctx, subsystem, hash).await?;
+						if !subsystem.sync_oracle.is_major_syncing() {
+							// If we're major syncing, processing finalized
+							// blocks might take quite a very long time
+							// and make the subsystem unresponsive.
+							process_block_activated(ctx, subsystem, hash).await?;
+						}
 					}
 					subsystem.finalized_number = Some(number);
 					subsystem.known_blocks.prune_finalized(number);
diff --git a/node/core/av-store/src/tests.rs b/node/core/av-store/src/tests.rs
index 9efd410ebac2..e26a3507480b 100644
--- a/node/core/av-store/src/tests.rs
+++ b/node/core/av-store/src/tests.rs
@@ -103,6 +103,18 @@ impl Default for TestState {
 	}
 }
 
+struct NoSyncOracle;
+
+impl sp_consensus::SyncOracle for NoSyncOracle {
+	fn is_major_syncing(&self) -> bool {
+		false
+	}
+
+	fn is_offline(&self) -> bool {
+		unimplemented!("not used")
+	}
+}
+
 fn test_harness<T: Future<Output = VirtualOverseer>>(
 	state: TestState,
 	store: Arc<dyn Database>,
@@ -122,6 +134,7 @@ fn test_harness<T: Future<Output = VirtualOverseer>>(
 		TEST_CONFIG,
 		state.pruning_config.clone(),
 		Box::new(state.clock),
+		Box::new(NoSyncOracle),
 		Metrics::default(),
 	);
 
diff --git a/node/service/src/overseer.rs b/node/service/src/overseer.rs
index 7dff86693827..5b1c728724ab 100644
--- a/node/service/src/overseer.rs
+++ b/node/service/src/overseer.rs
@@ -231,6 +231,7 @@ where
 		.availability_store(AvailabilityStoreSubsystem::new(
 			parachains_db.clone(),
 			availability_config,
+			Box::new(network_service.clone()),
 			Metrics::register(registry)?,
 		))
 		.bitfield_distribution(BitfieldDistributionSubsystem::new(Metrics::register(registry)?))