diff --git a/src/main/java/org/qortal/block/BlockChain.java b/src/main/java/org/qortal/block/BlockChain.java
index 8f6ddab7..95ecc41b 100644
--- a/src/main/java/org/qortal/block/BlockChain.java
+++ b/src/main/java/org/qortal/block/BlockChain.java
@@ -567,6 +567,7 @@ public class BlockChain {
 					--height;
 					orphanBlockData = repository.getBlockRepository().fromHeight(height);
 
+					repository.discardChanges(); // clear transaction status to prevent deadlocks
 					Controller.getInstance().onNewBlock(orphanBlockData);
 				}
 
diff --git a/src/main/java/org/qortal/controller/BlockMinter.java b/src/main/java/org/qortal/controller/BlockMinter.java
index aa80246d..46a29cf9 100644
--- a/src/main/java/org/qortal/controller/BlockMinter.java
+++ b/src/main/java/org/qortal/controller/BlockMinter.java
@@ -306,8 +306,10 @@ public class BlockMinter extends Thread {
 				}
 
 				if (newBlockMinted) {
-					BlockData newBlockData = newBlock.getBlockData();
 					// Notify Controller and broadcast our new chain to network
+					BlockData newBlockData = newBlock.getBlockData();
+
+					repository.discardChanges(); // clear transaction status to prevent deadlocks
 					Controller.getInstance().onNewBlock(newBlockData);
 
 					Network network = Network.getInstance();
diff --git a/src/main/java/org/qortal/controller/Controller.java b/src/main/java/org/qortal/controller/Controller.java
index 2683fb2d..406fda79 100644
--- a/src/main/java/org/qortal/controller/Controller.java
+++ b/src/main/java/org/qortal/controller/Controller.java
@@ -835,6 +835,12 @@ public class Controller extends Thread {
 		}
 	}
 
+	/**
+	 * Callback for when we've received a new block.
+	 * <p>
+	 * See <b>WARNING</b> for {@link EventBus#notify(Event)}
+	 * to prevent deadlocks.
+	 */
 	public void onNewBlock(BlockData latestBlockData) {
 		// Protective copy
 		BlockData blockDataCopy = new BlockData(latestBlockData);
diff --git a/src/main/java/org/qortal/controller/Synchronizer.java b/src/main/java/org/qortal/controller/Synchronizer.java
index 8dca5b05..5af2030d 100644
--- a/src/main/java/org/qortal/controller/Synchronizer.java
+++ b/src/main/java/org/qortal/controller/Synchronizer.java
@@ -410,6 +410,7 @@ public class Synchronizer {
 			--ourHeight;
 			orphanBlockData = repository.getBlockRepository().fromHeight(ourHeight);
 
+			repository.discardChanges(); // clear transaction status to prevent deadlocks
 			Controller.getInstance().onNewBlock(orphanBlockData);
 		}
 
diff --git a/src/main/java/org/qortal/event/EventBus.java b/src/main/java/org/qortal/event/EventBus.java
index e0014a20..63c80143 100644
--- a/src/main/java/org/qortal/event/EventBus.java
+++ b/src/main/java/org/qortal/event/EventBus.java
@@ -20,6 +20,21 @@ public enum EventBus {
 		}
 	}
 
+	/**
+	 * <b>WARNING:</b> before calling this method,
+	 * make sure repository holds no locks, e.g. by calling
+	 * <tt>repository.discardChanges()</tt>.
+	 * <p>
+	 * This is because event listeners might open a new
+	 * repository session which will deadlock HSQLDB
+	 * if it tries to CHECKPOINT.
+	 * <p>
+	 * The HSQLDB deadlock occurs because the caller's
+	 * repository session blocks the CHECKPOINT until
+	 * their transaction is closed, yet event listeners
+	 * new sessions are blocked until CHECKPOINT is
+	 * completed, hence deadlock.
+	 */
 	public void notify(Event event) {
 		List<Listener> clonedListeners;