diff --git a/lib/pubsub/subscription.js b/lib/pubsub/subscription.js
index 66a193161447..668dd2bb03f2 100644
--- a/lib/pubsub/subscription.js
+++ b/lib/pubsub/subscription.js
@@ -127,7 +127,7 @@ function Subscription(pubsub, options) {
   this.autoAck = util.is(options.autoAck, 'boolean') ? options.autoAck : false;
   this.closed = false;
   this.interval = util.is(options.interval, 'number') ? options.interval : 10;
-  this.inProgress = 0;
+  this.inProgressAckIds = {};
   this.maxInProgress =
     util.is(options.maxInProgress, 'number') ? options.maxInProgress : Infinity;
   this.messageListeners = 0;
@@ -243,7 +243,7 @@ Subscription.prototype.startPulling_ = function() {
   var maxResults;
 
   if (this.maxInProgress < Infinity) {
-    maxResults = this.maxInProgress - this.inProgress;
+    maxResults = this.maxInProgress - Object.keys(this.inProgressAckIds).length;
   }
 
   this.pull({
@@ -284,8 +284,10 @@ Subscription.prototype.ack = function(ackIds, callback) {
         'At least one ID must be specified before it can be acknowledged.');
   }
 
+  ackIds = util.arrayize(ackIds);
+
   var body = {
-    ackIds: util.arrayize(ackIds)
+    ackIds: ackIds
   };
 
   callback = callback || util.noop;
@@ -293,7 +295,6 @@ Subscription.prototype.ack = function(ackIds, callback) {
   var path = this.name + ':acknowledge';
 
   this.makeReq_('POST', path, null, body, function() {
-    self.inProgress--;
     self.refreshPausedStatus_();
     callback.apply(self, arguments);
   });
@@ -391,9 +392,10 @@ Subscription.prototype.pull = function(options, callback) {
     }
 
     var messages = response.receivedMessages || [];
-    messages = messages.map(Subscription.formatMessage_);
+    messages = messages
+      .map(Subscription.formatMessage_)
+      .map(self.decorateMessage_.bind(self));
 
-    self.inProgress += messages.length;
     self.refreshPausedStatus_();
 
     if (self.autoAck && messages.length !== 0) {
@@ -441,9 +443,25 @@ Subscription.prototype.setAckDeadline = function(options, callback) {
   this.makeReq_('POST', path, null, body, callback);
 };
 
+Subscription.prototype.decorateMessage_ = function(message) {
+  var self = this;
+
+  this.inProgressAckIds[message.ackId] = true;
+
+  message.ack = self.ack.bind(self, message.ackId);
+
+  message.skip = function() {
+    delete self.inProgressAckIds[message.ackId];
+    self.refreshPausedStatus_();
+  };
+
+  return message;
+};
+
 Subscription.prototype.refreshPausedStatus_ = function() {
   var isCurrentlyPaused = this.paused;
-  this.paused = this.inProgress >= this.maxInProgress;
+  var inProgress = Object.keys(this.inProgressAckIds).length;
+  this.paused = inProgress >= this.maxInProgress;
 
   if (isCurrentlyPaused && !this.paused && this.messageListeners > 0) {
     this.startPulling_();