diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/extensions/events/PrivateStateChanged.java b/gerrit-server/src/main/java/com/google/gerrit/server/extensions/events/PrivateStateChanged.java
index 37c90896f9..843b082400 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/extensions/events/PrivateStateChanged.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/extensions/events/PrivateStateChanged.java
@@ -23,10 +23,12 @@ import com.google.gerrit.reviewdb.client.Account;
 import com.google.gerrit.reviewdb.client.Change;
 import com.google.gwtorm.server.OrmException;
 import com.google.inject.Inject;
+import com.google.inject.Singleton;
 import java.sql.Timestamp;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+@Singleton
 public class PrivateStateChanged {
   private static final Logger log = LoggerFactory.getLogger(PrivateStateChanged.class);
 
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/extensions/events/WorkInProgressStateChanged.java b/gerrit-server/src/main/java/com/google/gerrit/server/extensions/events/WorkInProgressStateChanged.java
index 7290b27f59..94a9dd95e7 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/extensions/events/WorkInProgressStateChanged.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/extensions/events/WorkInProgressStateChanged.java
@@ -23,10 +23,12 @@ import com.google.gerrit.reviewdb.client.Account;
 import com.google.gerrit.reviewdb.client.Change;
 import com.google.gwtorm.server.OrmException;
 import com.google.inject.Inject;
+import com.google.inject.Singleton;
 import java.sql.Timestamp;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+@Singleton
 public class WorkInProgressStateChanged {
   private static final Logger log = LoggerFactory.getLogger(WorkInProgressStateChanged.class);