diff --git a/node/core/dispute-coordinator/src/tests.rs b/node/core/dispute-coordinator/src/tests.rs
index afd97bc2734c..ba8254b4c463 100644
--- a/node/core/dispute-coordinator/src/tests.rs
+++ b/node/core/dispute-coordinator/src/tests.rs
@@ -55,7 +55,9 @@ use polkadot_node_subsystem::{
 	messages::{AllMessages, BlockDescription, RuntimeApiMessage, RuntimeApiRequest},
 	ActivatedLeaf, ActiveLeavesUpdate, LeafStatus,
 };
-use polkadot_node_subsystem_test_helpers::{make_subsystem_context, TestSubsystemContextHandle};
+use polkadot_node_subsystem_test_helpers::{
+	make_buffered_subsystem_context, TestSubsystemContextHandle,
+};
 use polkadot_primitives::v2::{
 	ApprovalVote, BlockNumber, CandidateCommitments, CandidateEvent, CandidateHash,
 	CandidateReceipt, CoreIndex, DisputeStatement, GroupIndex, Hash, HeadData, Header, IndexedVec,
@@ -523,7 +525,7 @@ impl TestState {
 		F: FnOnce(TestState, VirtualOverseer) -> BoxFuture<'static, TestState>,
 	{
 		self.known_session = None;
-		let (ctx, ctx_handle) = make_subsystem_context(TaskExecutor::new());
+		let (ctx, ctx_handle) = make_buffered_subsystem_context(TaskExecutor::new(), 1);
 		let subsystem = DisputeCoordinatorSubsystem::new(
 			self.db.clone(),
 			self.config.clone(),
diff --git a/node/subsystem-test-helpers/src/lib.rs b/node/subsystem-test-helpers/src/lib.rs
index 30ab5c830c2a..dd207039091a 100644
--- a/node/subsystem-test-helpers/src/lib.rs
+++ b/node/subsystem-test-helpers/src/lib.rs
@@ -280,11 +280,22 @@ impl<M> TestSubsystemContextHandle<M> {
 	}
 }
 
-/// Make a test subsystem context.
+/// Make a test subsystem context with `buffer_size == 0`. This is used by most
+/// of the tests.
 pub fn make_subsystem_context<M, S>(
 	spawner: S,
 ) -> (TestSubsystemContext<M, SpawnGlue<S>>, TestSubsystemContextHandle<M>) {
-	let (overseer_tx, overseer_rx) = mpsc::channel(1);
+	make_buffered_subsystem_context(spawner, 0)
+}
+
+/// Make a test subsystem context with buffered overseer channel. Some tests (e.g.
+/// `dispute-coordinator`) create too many parallel operations and deadlock unless
+/// the channel is buffered. Usually `buffer_size=1` is enough.
+pub fn make_buffered_subsystem_context<M, S>(
+	spawner: S,
+	buffer_size: usize,
+) -> (TestSubsystemContext<M, SpawnGlue<S>>, TestSubsystemContextHandle<M>) {
+	let (overseer_tx, overseer_rx) = mpsc::channel(buffer_size);
 	let (all_messages_tx, all_messages_rx) = mpsc::unbounded();
 
 	(