@@ -88,7 +88,7 @@ class MessageDispatcher {
   // it is not modified while inside the queue.
   // The hashcode and equals methods are explicitly not implemented to discourage
   // the use of this class as keys in maps or similar containers.
-  private static class ExtensionJob implements Comparable<ExtensionJob> {
+  private class ExtensionJob implements Comparable<ExtensionJob> {
     Instant creation;
     Instant expiration;
     int nextExtensionSeconds;
@@ -106,7 +106,9 @@ private static class ExtensionJob implements Comparable<ExtensionJob> {
     }
 
     void extendExpiration(Instant now) {
-      expiration = now.plus(Duration.standardSeconds(nextExtensionSeconds));
+      Instant possibleExtension = now.plus(Duration.standardSeconds(nextExtensionSeconds));
+      Instant maxExtension = creation.plus(maxAckExtensionPeriod);
+      expiration = possibleExtension.isBefore(maxExtension) ? possibleExtension : maxExtension;
       nextExtensionSeconds = Math.min(2 * nextExtensionSeconds, MAX_ACK_DEADLINE_EXTENSION_SECS);
     }
 
 
@@ -278,7 +278,7 @@ public void testModifyAckDeadline() throws Exception {
         startSubscriber(
             getTestSubscriberBuilder(testReceiver)
                 .setAckExpirationPadding(Duration.standardSeconds(1))
-                .setMaxAckExtensionPeriod(Duration.standardSeconds(12)));
+                .setMaxAckExtensionPeriod(Duration.standardSeconds(13)));
     // Send messages to be acked
     List<String> testAckIdsBundle = ImmutableList.of("A", "B", "C");
     testReceiver.setExplicitAck(true);
@@ -306,7 +306,9 @@ public ModifyAckDeadline apply(String ack) {
         new Function<String, ModifyAckDeadline>() {
           @Override
           public ModifyAckDeadline apply(String ack) {
-            return new ModifyAckDeadline(ack, 4);
+            return new ModifyAckDeadline(ack, 2); // It is expected that the deadline is renewed
+                                                  // only two more seconds to not pass the max
+                                                  // ack deadline ext.
           }
         });