diff --git a/bramble-core/src/main/java/org/briarproject/bramble/connection/DuplexSyncConnection.java b/bramble-core/src/main/java/org/briarproject/bramble/connection/DuplexSyncConnection.java
index 0ed62ab0b..55be56812 100644
--- a/bramble-core/src/main/java/org/briarproject/bramble/connection/DuplexSyncConnection.java
+++ b/bramble-core/src/main/java/org/briarproject/bramble/connection/DuplexSyncConnection.java
@@ -21,6 +21,7 @@ import java.io.IOException;
 import java.util.concurrent.Executor;
 
 import javax.annotation.Nullable;
+import javax.annotation.concurrent.GuardedBy;
 
 import static org.briarproject.bramble.api.nullsafety.NullSafety.requireNonNull;
 
@@ -33,8 +34,30 @@ abstract class DuplexSyncConnection extends SyncConnection {
 	final TransportConnectionWriter writer;
 	final TransportProperties remote;
 
+	private final Object interruptLock = new Object();
+
+	@GuardedBy("interruptLock")
 	@Nullable
-	volatile SyncSession outgoingSession = null;
+	private SyncSession outgoingSession = null;
+	@GuardedBy("interruptLock")
+	private boolean interruptWaiting = false;
+
+	void interruptOutgoingSession() {
+		synchronized (interruptLock) {
+			if (outgoingSession == null) interruptWaiting = true;
+			else outgoingSession.interrupt();
+		}
+	}
+
+	void setOutgoingSession(SyncSession outgoingSession) {
+		synchronized (interruptLock) {
+			this.outgoingSession = outgoingSession;
+			if (interruptWaiting) {
+				outgoingSession.interrupt();
+				interruptWaiting = false;
+			}
+		}
+	}
 
 	DuplexSyncConnection(KeyManager keyManager,
 			ConnectionRegistry connectionRegistry,
@@ -57,9 +80,7 @@ abstract class DuplexSyncConnection extends SyncConnection {
 	void onReadError(boolean recognised) {
 		disposeOnError(reader, recognised);
 		disposeOnError(writer);
-		// Interrupt the outgoing session so it finishes
-		SyncSession out = outgoingSession;
-		if (out != null) out.interrupt();
+		interruptOutgoingSession();
 	}
 
 	void onWriteError() {
diff --git a/bramble-core/src/main/java/org/briarproject/bramble/connection/IncomingDuplexSyncConnection.java b/bramble-core/src/main/java/org/briarproject/bramble/connection/IncomingDuplexSyncConnection.java
index 382b17a50..ba780cbc5 100644
--- a/bramble-core/src/main/java/org/briarproject/bramble/connection/IncomingDuplexSyncConnection.java
+++ b/bramble-core/src/main/java/org/briarproject/bramble/connection/IncomingDuplexSyncConnection.java
@@ -68,9 +68,7 @@ class IncomingDuplexSyncConnection extends DuplexSyncConnection
 			// Create and run the incoming session
 			createIncomingSession(ctx, reader).run();
 			reader.dispose(false, true);
-			// Interrupt the outgoing session so it finishes cleanly
-			SyncSession out = outgoingSession;
-			if (out != null) out.interrupt();
+			interruptOutgoingSession();
 		} catch (DbException | IOException e) {
 			logException(LOG, WARNING, e);
 			onReadError(true);
@@ -91,7 +89,7 @@ class IncomingDuplexSyncConnection extends DuplexSyncConnection
 		try {
 			// Create and run the outgoing session
 			SyncSession out = createDuplexOutgoingSession(ctx, writer);
-			outgoingSession = out;
+			setOutgoingSession(out);
 			out.run();
 			writer.dispose(false);
 		} catch (IOException e) {
diff --git a/bramble-core/src/main/java/org/briarproject/bramble/connection/OutgoingDuplexSyncConnection.java b/bramble-core/src/main/java/org/briarproject/bramble/connection/OutgoingDuplexSyncConnection.java
index 0c8f464fb..ed6d21d05 100644
--- a/bramble-core/src/main/java/org/briarproject/bramble/connection/OutgoingDuplexSyncConnection.java
+++ b/bramble-core/src/main/java/org/briarproject/bramble/connection/OutgoingDuplexSyncConnection.java
@@ -60,7 +60,7 @@ class OutgoingDuplexSyncConnection extends DuplexSyncConnection
 		try {
 			// Create and run the outgoing session
 			SyncSession out = createDuplexOutgoingSession(ctx, writer);
-			outgoingSession = out;
+			setOutgoingSession(out);
 			out.run();
 			writer.dispose(false);
 		} catch (IOException e) {
@@ -104,9 +104,7 @@ class OutgoingDuplexSyncConnection extends DuplexSyncConnection
 			// Create and run the incoming session
 			createIncomingSession(ctx, reader).run();
 			reader.dispose(false, true);
-			// Interrupt the outgoing session so it finishes cleanly
-			SyncSession out = outgoingSession;
-			if (out != null) out.interrupt();
+			interruptOutgoingSession();
 		} catch (DbException | IOException e) {
 			logException(LOG, WARNING, e);
 			onReadError();