diff --git a/gerrit-cache-h2/src/main/java/com/google/gerrit/server/cache/h2/H2CacheImpl.java b/gerrit-cache-h2/src/main/java/com/google/gerrit/server/cache/h2/H2CacheImpl.java
index a5bdacc77b..9da1afcc2f 100644
--- a/gerrit-cache-h2/src/main/java/com/google/gerrit/server/cache/h2/H2CacheImpl.java
+++ b/gerrit-cache-h2/src/main/java/com/google/gerrit/server/cache/h2/H2CacheImpl.java
@@ -277,8 +277,12 @@ public class H2CacheImpl<K, V> extends AbstractLoadingCache<K, V> {
           try {
             ObjectOutputStream ser =
                 new ObjectOutputStream(new SinkOutputStream(into));
-            ser.writeObject(from);
-            ser.flush();
+            try {
+              ser.writeObject(from);
+              ser.flush();
+            } finally {
+              ser.close();
+            }
           } catch (IOException err) {
             throw new RuntimeException("Cannot hash as Serializable", err);
           }