diff --git a/packages/pubsub/src/subscription.js b/packages/pubsub/src/subscription.js
index 0193f81ac71..685b46ff1c5 100644
--- a/packages/pubsub/src/subscription.js
+++ b/packages/pubsub/src/subscription.js
@@ -320,13 +320,17 @@ Subscription.prototype.ack_ = function(message) {
 Subscription.prototype.breakLease_ = function(message) {
   var messageIndex = this.inventory_.lease.indexOf(message.ackId);
 
+  if (messageIndex === -1) {
+    return;
+  }
+
   this.inventory_.lease.splice(messageIndex, 1);
   this.inventory_.bytes -= message.length;
 
-  if (this.connectionPool) {
-    if (this.connectionPool.isPaused && !this.hasMaxMessages_()) {
-      this.connectionPool.resume();
-    }
+  var pool = this.connectionPool;
+
+  if (pool && pool.isPaused && !this.hasMaxMessages_()) {
+    pool.resume();
   }
 
   if (!this.inventory_.lease.length) {
@@ -730,7 +734,7 @@ Subscription.prototype.getMetadata = function(gaxOpts, callback) {
  * @return {boolean}
  */
 Subscription.prototype.hasMaxMessages_ = function() {
-  return this.inventory_.lease.length >= this.flowControl.maxMessages ||
+  return this.inventory_.lease.length > this.flowControl.maxMessages ||
     this.inventory_.bytes >= this.flowControl.maxBytes;
 };
 
@@ -888,11 +892,16 @@ Subscription.prototype.openConnection_ = function() {
   });
 
   pool.on('message', function(message) {
-    self.emit('message', self.leaseMessage_(message));
+    if (!self.hasMaxMessages_()) {
+      self.emit('message', self.leaseMessage_(message));
+      return;
+    }
 
-    if (self.hasMaxMessages_() && !pool.isPaused) {
+    if (!pool.isPaused) {
       pool.pause();
     }
+
+    message.nack();
   });
 
   pool.once('connected', function() {
diff --git a/packages/pubsub/system-test/pubsub.js b/packages/pubsub/system-test/pubsub.js
index ff49e59388c..58e59c2ca5f 100644
--- a/packages/pubsub/system-test/pubsub.js
+++ b/packages/pubsub/system-test/pubsub.js
@@ -479,6 +479,30 @@ describe('pubsub', function() {
         setTimeout(() => subscription.close(done), 2500);
       }
     });
+
+    it('should respect flow control limits', function(done) {
+      var maxMessages = 3;
+      var messageCount = 0;
+
+      var subscription = topic.subscription(SUB_NAMES[0], {
+        flowControl: {
+          maxMessages: maxMessages
+        }
+      });
+
+      subscription.on('error', done);
+      subscription.on('message', onMessage);
+
+      function onMessage() {
+        if (++messageCount < (maxMessages + 1)) {
+          return;
+        }
+
+        setImmediate(function() {
+          subscription.close(done);
+        });
+      }
+    });
   });
 
   describe('IAM', function() {
diff --git a/packages/pubsub/test/connection-pool.js b/packages/pubsub/test/connection-pool.js
index 2fb5097634f..b4fe57da855 100644
--- a/packages/pubsub/test/connection-pool.js
+++ b/packages/pubsub/test/connection-pool.js
@@ -1170,13 +1170,22 @@ describe('ConnectionPool', function() {
     });
 
     it('should reset internal used props', function() {
+      var fakeDate = Date.now();
+      var dateNow = Date.now;
+
+      global.Date.now = function() {
+        return fakeDate;
+      };
+
       pool.failedConnectionAttempts = 100;
       pool.noConnectionsTime = 0;
 
       pool.open();
 
       assert.strictEqual(pool.failedConnectionAttempts, 0);
-      assert.strictEqual(pool.noConnectionsTime, Date.now());
+      assert.strictEqual(pool.noConnectionsTime, fakeDate);
+
+      global.Date.now = dateNow;
     });
 
     it('should listen for newListener events', function() {
diff --git a/packages/pubsub/test/subscription.js b/packages/pubsub/test/subscription.js
index 192421fd7d4..b2d206c501d 100644
--- a/packages/pubsub/test/subscription.js
+++ b/packages/pubsub/test/subscription.js
@@ -407,6 +407,19 @@ describe('Subscription', function() {
       assert.strictEqual(subscription.inventory_.bytes, 0);
     });
 
+    it('should noop for unknown messages', function() {
+      var message = {
+        ackId: 'def',
+        data: new Buffer('world'),
+        length: 5
+      };
+
+      subscription.breakLease_(message);
+
+      assert.strictEqual(subscription.inventory_.lease.length, 1);
+      assert.strictEqual(subscription.inventory_.bytes, 5);
+    });
+
     describe('with connection pool', function() {
       it('should resume receiving messages if paused', function(done) {
         subscription.connectionPool = {
@@ -1174,9 +1187,9 @@ describe('Subscription', function() {
   });
 
   describe('hasMaxMessages_', function() {
-    it('should return true if the number of leases == maxMessages', function() {
+    it('should return true if the number of leases > maxMessages', function() {
       subscription.inventory_.lease = ['a', 'b', 'c'];
-      subscription.flowControl.maxMessages = 3;
+      subscription.flowControl.maxMessages = 2;
 
       assert(subscription.hasMaxMessages_());
     });
@@ -1473,7 +1486,7 @@ describe('Subscription', function() {
     });
 
     it('should pause the pool if sub is at max messages', function(done) {
-      var message = {};
+      var message = { nack: fakeUtil.noop };
       var leasedMessage = {};
 
       subscription.leaseMessage_ = function() {
@@ -1491,7 +1504,7 @@ describe('Subscription', function() {
     });
 
     it('should not re-pause the pool', function(done) {
-      var message = {};
+      var message = { nack: fakeUtil.noop };
       var leasedMessage = {};
 
       subscription.leaseMessage_ = function() {
@@ -1513,6 +1526,23 @@ describe('Subscription', function() {
       done();
     });
 
+    it('should nack messages if over limit', function(done) {
+      var message = { nack: done };
+      var leasedMessage = {};
+
+      subscription.leaseMessage_ = function() {
+        return leasedMessage;
+      };
+
+      subscription.hasMaxMessages_ = function() {
+        return true;
+      };
+
+      subscription.openConnection_();
+      subscription.connectionPool.isPaused = true;
+      subscription.connectionPool.emit('message', message);
+    });
+
     it('should flush the queue when connected', function(done) {
       subscription.flushQueues_ = done;