diff --git a/apps/dhcprelay/src/main/java/org/onosproject/dhcprelay/Dhcp4HandlerImpl.java b/apps/dhcprelay/src/main/java/org/onosproject/dhcprelay/Dhcp4HandlerImpl.java
index 731090d..90aafdd 100644
--- a/apps/dhcprelay/src/main/java/org/onosproject/dhcprelay/Dhcp4HandlerImpl.java
+++ b/apps/dhcprelay/src/main/java/org/onosproject/dhcprelay/Dhcp4HandlerImpl.java
@@ -20,6 +20,7 @@
 import com.google.common.collect.HashMultimap;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.Multimap;
+import com.google.common.collect.Multimaps;
 import com.google.common.collect.Sets;
 import org.apache.felix.scr.annotations.Activate;
 import org.apache.felix.scr.annotations.Component;
@@ -170,7 +171,7 @@
 
     protected HostProviderService providerService;
     protected ApplicationId appId;
-    protected Multimap<DeviceId, VlanId> ignoredVlans = HashMultimap.create();
+    protected Multimap<DeviceId, VlanId> ignoredVlans = Multimaps.synchronizedMultimap(HashMultimap.create());
     private InternalHostListener hostListener = new InternalHostListener();
 
     private List<DhcpServerInfo> defaultServerInfoList = new CopyOnWriteArrayList<>();