diff --git a/src/main/java/com/googlesource/gerrit/plugins/multisite/Configuration.java b/src/main/java/com/googlesource/gerrit/plugins/multisite/Configuration.java
index 8bb2a8b..88ab53e 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/multisite/Configuration.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/multisite/Configuration.java
@@ -25,6 +25,7 @@
 import com.google.inject.Inject;
 import com.google.inject.Singleton;
 import com.googlesource.gerrit.plugins.multisite.forwarder.events.EventFamily;
+import com.googlesource.gerrit.plugins.multisite.validation.dfsrefdb.zookeeper.ZkSharedRefDatabase;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.HashMap;
@@ -422,6 +423,7 @@
     private final int DEFAULT_CAS_RETRY_POLICY_BASE_SLEEP_TIME_MS = 100;
     private final int DEFAULT_CAS_RETRY_POLICY_MAX_SLEEP_TIME_MS = 300;
     private final int DEFAULT_CAS_RETRY_POLICY_MAX_RETRIES = 3;
+    private final boolean DEFAULT_MIGRATE = false;
 
     static {
       CuratorFrameworkFactory.Builder b = CuratorFrameworkFactory.builder();
@@ -441,6 +443,7 @@
     public final String KEY_CAS_RETRY_POLICY_BASE_SLEEP_TIME_MS = "casRetryPolicyBaseSleepTimeMs";
     public final String KEY_CAS_RETRY_POLICY_MAX_SLEEP_TIME_MS = "casRetryPolicyMaxSleepTimeMs";
     public final String KEY_CAS_RETRY_POLICY_MAX_RETRIES = "casRetryPolicyMaxRetries";
+    public static final String KEY_MIGRATE = "migrate";
 
     private final String connectionString;
     private final String root;
@@ -452,6 +455,7 @@
     private final int casBaseSleepTimeMs;
     private final int casMaxSleepTimeMs;
     private final int casMaxRetries;
+    private final boolean migrate;
 
     private CuratorFramework build;
 
@@ -518,6 +522,8 @@
               KEY_CAS_RETRY_POLICY_MAX_RETRIES,
               DEFAULT_CAS_RETRY_POLICY_MAX_RETRIES);
 
+      migrate = getBoolean(cfg, SplitBrain.SECTION, SUBSECTION, KEY_MIGRATE, DEFAULT_MIGRATE);
+
       checkArgument(StringUtils.isNotEmpty(connectionString), "zookeeper.%s contains no servers");
     }
 
@@ -542,6 +548,12 @@
       return new BoundedExponentialBackoffRetry(
           casBaseSleepTimeMs, casMaxSleepTimeMs, casMaxRetries);
     }
+
+    public ZkSharedRefDatabase.OperationMode getOperationMode() {
+      return migrate
+          ? ZkSharedRefDatabase.OperationMode.MIGRATION
+          : ZkSharedRefDatabase.OperationMode.NORMAL;
+    }
   }
 
   public static class SplitBrain {
diff --git a/src/main/java/com/googlesource/gerrit/plugins/multisite/validation/dfsrefdb/zookeeper/ZkSharedRefDatabase.java b/src/main/java/com/googlesource/gerrit/plugins/multisite/validation/dfsrefdb/zookeeper/ZkSharedRefDatabase.java
index c1272a7..86be4f5 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/multisite/validation/dfsrefdb/zookeeper/ZkSharedRefDatabase.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/multisite/validation/dfsrefdb/zookeeper/ZkSharedRefDatabase.java
@@ -35,11 +35,21 @@
   private final CuratorFramework client;
   private final RetryPolicy retryPolicy;
 
+  private final OperationMode operationMode;
+
+  public enum OperationMode {
+    NORMAL,
+    MIGRATION;
+  }
+
   @Inject
   public ZkSharedRefDatabase(
-      CuratorFramework client, @Named("ZkLockRetryPolicy") RetryPolicy retryPolicy) {
+      CuratorFramework client,
+      @Named("ZkLockRetryPolicy") RetryPolicy retryPolicy,
+      OperationMode operationMode) {
     this.client = client;
     this.retryPolicy = retryPolicy;
+    this.operationMode = operationMode;
   }
 
   @Override
@@ -62,6 +72,15 @@
           distributedRefValue.compareAndSet(
               writeObjectId(oldRef.getObjectId()), writeObjectId(newValue));
 
+      if (!newDistributedValue.succeeded()
+          && operationMode == OperationMode.MIGRATION
+          && refNotInZk(projectName, oldRef, newRef)) {
+        logger.atInfo().log(
+            "Missing entry in ZK for ref at path '%'. Assuming this is because we are in migration mode and creating it",
+            pathFor(projectName, oldRef, newRef));
+
+        return distributedRefValue.initialize(writeObjectId(newRef.getObjectId()));
+      }
       return newDistributedValue.succeeded();
     } catch (Exception e) {
       logger.atWarning().withCause(e).log(
@@ -73,6 +92,10 @@
     }
   }
 
+  private boolean refNotInZk(String projectName, Ref oldRef, Ref newRef) throws Exception {
+    return client.checkExists().forPath(pathFor(projectName, oldRef, newRef)) == null;
+  }
+
   static String pathFor(String projectName, Ref oldRef, Ref newRef) {
     return pathFor(projectName, MoreObjects.firstNonNull(oldRef.getName(), newRef.getName()));
   }
diff --git a/src/main/java/com/googlesource/gerrit/plugins/multisite/validation/dfsrefdb/zookeeper/ZkValidationModule.java b/src/main/java/com/googlesource/gerrit/plugins/multisite/validation/dfsrefdb/zookeeper/ZkValidationModule.java
index d4a3126..0b6b457 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/multisite/validation/dfsrefdb/zookeeper/ZkValidationModule.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/multisite/validation/dfsrefdb/zookeeper/ZkValidationModule.java
@@ -36,5 +36,7 @@
     bind(RetryPolicy.class)
         .annotatedWith(Names.named("ZkLockRetryPolicy"))
         .toInstance(cfg.getSplitBrain().getZookeeper().buildCasRetryPolicy());
+    bind(ZkSharedRefDatabase.OperationMode.class)
+        .toInstance(cfg.getSplitBrain().getZookeeper().getOperationMode());
   }
 }
diff --git a/src/main/resources/Documentation/config.md b/src/main/resources/Documentation/config.md
index ca3f87c..76f9ee9 100644
--- a/src/main/resources/Documentation/config.md
+++ b/src/main/resources/Documentation/config.md
@@ -211,6 +211,14 @@
 :   Configuration for the max number of retries to use to create the BoundedExponentialBackoffRetry policy
 used for the Compare and Swap operations on Zookeeper
     Defaults: 3
+
+```split-brain.zookeeper.migrate```
+:   Set to true when the plugin has been applied to an already existing module and
+there are no entries in Zookeeper for the existing refs. It will handle update failures
+caused by the old refs not existing forcing the creation of the new one
+    Defaults: false
+    
+
     
 #### Custom kafka properties:
 
diff --git a/src/test/java/com/googlesource/gerrit/plugins/multisite/validation/ValidationIT.java b/src/test/java/com/googlesource/gerrit/plugins/multisite/validation/ValidationIT.java
index fb63793..c65002a 100644
--- a/src/test/java/com/googlesource/gerrit/plugins/multisite/validation/ValidationIT.java
+++ b/src/test/java/com/googlesource/gerrit/plugins/multisite/validation/ValidationIT.java
@@ -70,7 +70,7 @@
 
     @Override
     protected void configure() {
-      ZookeeperTestContainerSupport zookeeperContainer = new ZookeeperTestContainerSupport();
+      ZookeeperTestContainerSupport zookeeperContainer = new ZookeeperTestContainerSupport(true);
       Configuration multiSiteConfig = zookeeperContainer.getConfig();
       bind(Configuration.class).toInstance(multiSiteConfig);
       install(new Module(multiSiteConfig, noteDb));
@@ -91,10 +91,8 @@
 
   @Test
   public void inSyncChangeValidatorShouldAcceptNewChange() throws Exception {
-    // FIXME: The code does not work for already existing refs (need a migration step for first
-    // run - T0). Using "refs/heads/master2" in this test for now
     final PushOneCommit.Result change =
-        createCommitAndPush(testRepo, "refs/heads/master2", "msg", "file", "content");
+        createCommitAndPush(testRepo, "refs/heads/master", "msg", "file", "content");
 
     change.assertOkStatus();
   }
diff --git a/src/test/java/com/googlesource/gerrit/plugins/multisite/validation/dfsrefdb/zookeeper/ZkSharedRefDatabaseTest.java b/src/test/java/com/googlesource/gerrit/plugins/multisite/validation/dfsrefdb/zookeeper/ZkSharedRefDatabaseTest.java
index b5ac1e4..88548f4 100644
--- a/src/test/java/com/googlesource/gerrit/plugins/multisite/validation/dfsrefdb/zookeeper/ZkSharedRefDatabaseTest.java
+++ b/src/test/java/com/googlesource/gerrit/plugins/multisite/validation/dfsrefdb/zookeeper/ZkSharedRefDatabaseTest.java
@@ -47,9 +47,12 @@
 
   @Before
   public void setup() {
-    zookeeperContainer = new ZookeeperTestContainerSupport();
+    zookeeperContainer = new ZookeeperTestContainerSupport(false);
     zkSharedRefDatabase =
-        new ZkSharedRefDatabase(zookeeperContainer.getCurator(), new RetryNTimes(5, 30));
+        new ZkSharedRefDatabase(
+            zookeeperContainer.getCurator(),
+            new RetryNTimes(5, 30),
+            ZkSharedRefDatabase.OperationMode.NORMAL);
   }
 
   @After
@@ -59,12 +62,12 @@
 
   @Test
   public void shouldCompareAndCreateSuccessfully() throws Exception {
-  	Ref ref = refOf(AN_OBJECT_ID_1);
+    Ref ref = refOf(AN_OBJECT_ID_1);
 
-  	assertThat(zkSharedRefDatabase.compareAndCreate(A_TEST_PROJECT_NAME, ref)).isTrue();
+    assertThat(zkSharedRefDatabase.compareAndCreate(A_TEST_PROJECT_NAME, ref)).isTrue();
 
-  	assertThat(zookeeperContainer.readRefValueFromZk(A_TEST_PROJECT_NAME, ref))
-  			.isEqualTo(ref.getObjectId());
+    assertThat(zookeeperContainer.readRefValueFromZk(A_TEST_PROJECT_NAME, ref))
+        .isEqualTo(ref.getObjectId());
   }
 
   @Test
@@ -100,6 +103,24 @@
   }
 
   @Test
+  public void compareAndPutShouldDoAnInsertIfTheObjectionDoesNotExistAndInMigrationMode()
+      throws Exception {
+    zkSharedRefDatabase =
+        new ZkSharedRefDatabase(
+            zookeeperContainer.getCurator(),
+            new RetryNTimes(5, 30),
+            ZkSharedRefDatabase.OperationMode.MIGRATION);
+
+    Ref oldRef = refOf(AN_OBJECT_ID_1);
+    assertThat(
+            zkSharedRefDatabase.compareAndPut(A_TEST_PROJECT_NAME, oldRef, refOf(AN_OBJECT_ID_2)))
+        .isTrue();
+
+    assertThat(zookeeperContainer.readRefValueFromZk(A_TEST_PROJECT_NAME, oldRef))
+        .isEqualTo(AN_OBJECT_ID_2);
+  }
+
+  @Test
   public void shouldCompareAndRemoveSuccessfully() throws Exception {
     Ref oldRef = refOf(AN_OBJECT_ID_1);
     String projectName = A_TEST_PROJECT_NAME;
@@ -112,13 +133,12 @@
   @Test
   public void shouldReplaceTheRefWithATombstoneAfterCompareAndPutRemove() throws Exception {
     Ref oldRef = refOf(AN_OBJECT_ID_1);
-    String projectName = A_TEST_PROJECT_NAME;
 
-    zookeeperContainer.createRefInZk(projectName, oldRef);
+    zookeeperContainer.createRefInZk(A_TEST_PROJECT_NAME, oldRef);
 
-    assertThat(zkSharedRefDatabase.compareAndRemove(projectName, oldRef)).isTrue();
+    assertThat(zkSharedRefDatabase.compareAndRemove(A_TEST_PROJECT_NAME, oldRef)).isTrue();
 
-    assertThat(zookeeperContainer.readRefValueFromZk(projectName, oldRef))
+    assertThat(zookeeperContainer.readRefValueFromZk(A_TEST_PROJECT_NAME, oldRef))
         .isEqualTo(ObjectId.zeroId());
   }
 
diff --git a/src/test/java/com/googlesource/gerrit/plugins/multisite/validation/dfsrefdb/zookeeper/ZookeeperTestContainerSupport.java b/src/test/java/com/googlesource/gerrit/plugins/multisite/validation/dfsrefdb/zookeeper/ZookeeperTestContainerSupport.java
index 3d041ae..d479f7f 100644
--- a/src/test/java/com/googlesource/gerrit/plugins/multisite/validation/dfsrefdb/zookeeper/ZookeeperTestContainerSupport.java
+++ b/src/test/java/com/googlesource/gerrit/plugins/multisite/validation/dfsrefdb/zookeeper/ZookeeperTestContainerSupport.java
@@ -68,7 +68,7 @@
   }
 
   @SuppressWarnings("resource")
-  public ZookeeperTestContainerSupport() {
+  public ZookeeperTestContainerSupport(boolean migrationMode) {
     container = new ZookeeperContainer().withExposedPorts(2181).waitingFor(Wait.forListeningPort());
     container.start();
     Integer zkHostPort = container.getMappedPort(2181);
@@ -76,6 +76,16 @@
     String connectString = "localhost:" + zkHostPort;
     splitBrainconfig.setBoolean("split-brain", null, "enabled", true);
     splitBrainconfig.setString("split-brain", "zookeeper", "connectString", connectString);
+    splitBrainconfig.setString(
+        "split-brain",
+        Configuration.Zookeeper.SUBSECTION,
+        Configuration.Zookeeper.KEY_CONNECT_STRING,
+        connectString);
+    splitBrainconfig.setBoolean(
+        "split-brain",
+        Configuration.Zookeeper.SUBSECTION,
+        Configuration.Zookeeper.KEY_MIGRATE,
+        migrationMode);
 
     configuration = new Configuration(splitBrainconfig);
     this.curator = configuration.getSplitBrain().getZookeeper().buildCurator();