diff --git a/FastGithub.DomainResolve/DnsClient.cs b/FastGithub.DomainResolve/DnsClient.cs
index fe3b175..e97867b 100644
--- a/FastGithub.DomainResolve/DnsClient.cs
+++ b/FastGithub.DomainResolve/DnsClient.cs
@@ -265,12 +265,15 @@ namespace FastGithub.DomainResolve
                 return addresses;
             }
 
-            var hashSet = new HashSet<IPAddress> { fastedAddress };
+            var list = new List<IPAddress> { fastedAddress };
             foreach (var address in addresses)
             {
-                hashSet.Add(address);
+                if (address.Equals(fastedAddress) == false)
+                {
+                    list.Add(address);
+                }
             }
-            return hashSet.ToArray();
+            return list.ToArray();
         }
 
         /// <summary>
diff --git a/FastGithub.DomainResolve/IPAddressCollection.cs b/FastGithub.DomainResolve/IPAddressCollection.cs
index 2fc1122..9659161 100644
--- a/FastGithub.DomainResolve/IPAddressCollection.cs
+++ b/FastGithub.DomainResolve/IPAddressCollection.cs
@@ -41,7 +41,10 @@ namespace FastGithub.DomainResolve
         /// <returns></returns>
         public IPAddress[] ToArray()
         {
-            return this.ToItemArray().OrderBy(item => item.PingElapsed).Select(item => item.Address).ToArray();
+            lock (this.syncRoot)
+            {
+                return this.hashSet.OrderBy(item => item.PingElapsed).Select(item => item.Address).ToArray();
+            }
         }
 
         /// <summary>