diff --git a/hbase-server/src/main/java/org/apache/hadoop/hbase/master/ServerManager.java b/hbase-server/src/main/java/org/apache/hadoop/hbase/master/ServerManager.java
index 318a60784e3..09cfee1c21f 100644
--- a/hbase-server/src/main/java/org/apache/hadoop/hbase/master/ServerManager.java
+++ b/hbase-server/src/main/java/org/apache/hadoop/hbase/master/ServerManager.java
@@ -421,7 +421,9 @@ public class ServerManager {
    */
   public Map<ServerName, ServerLoad> getOnlineServers() {
     // Presumption is that iterating the returned Map is OK.
-    return Collections.unmodifiableMap(this.onlineServers);
+    synchronized (this.onlineServers) {
+      return Collections.unmodifiableMap(this.onlineServers);
+    }
   }