diff --git a/lib/membership.js b/lib/membership.js
index 5333dcee..20f9746c 100644
--- a/lib/membership.js
+++ b/lib/membership.js
@@ -29,6 +29,7 @@ var util = require('util');
 function Membership(ringpop) {
     this.ringpop = ringpop;
     this.members = [];
+    this.membersByAddress = {};
     this.checksum = null;
 }
 
@@ -59,16 +60,7 @@ Membership.prototype.computeChecksum = function computeChecksum() {
 };
 
 Membership.prototype.findMemberByAddress = function findMemberByAddress(address) {
-    // TODO Index by address
-    for (var i = 0; i < this.members.length; i++) {
-        var member = this.members[i];
-
-        if (member.address === address) {
-            return member;
-        }
-    }
-
-    return null;
+    return this.membersByAddress[address];
 };
 
 Membership.prototype.generateChecksumString = function generateChecksumString() {
@@ -249,6 +241,7 @@ Membership.prototype.update = function update(changes) {
             }
 
             self.members.splice(self.getJoinPosition(), 0, member);
+            self.membersByAddress[member.address] = member;
         }
 
         member.status = update.status;
diff --git a/test/integration/swim-test.js b/test/integration/swim-test.js
index 5cfe49b8..5f3c7f5d 100644
--- a/test/integration/swim-test.js
+++ b/test/integration/swim-test.js
@@ -190,7 +190,9 @@ testRingpopCluster({
     // Mutating all member addresses to make each of selected ping-req members
     // unreachable and therefore, the results of ping-req inconclusive.
     ringpop.membership.members.forEach(function eachMember(member) {
-        member.address += '001';
+        if (member.address !== unreachableMember.address) {
+            member.address += '001';
+        }
     });
 
     sendPingReq({