diff --git a/server/src/test/java/org/elasticsearch/action/admin/cluster/node/tasks/TestTaskPlugin.java b/server/src/test/java/org/elasticsearch/action/admin/cluster/node/tasks/TestTaskPlugin.java
index 63629e16974d5..2b25a9ab59ce1 100644
--- a/server/src/test/java/org/elasticsearch/action/admin/cluster/node/tasks/TestTaskPlugin.java
+++ b/server/src/test/java/org/elasticsearch/action/admin/cluster/node/tasks/TestTaskPlugin.java
@@ -300,12 +300,13 @@ protected NodeResponse nodeOperation(NodeRequest request, Task task) {
             logger.info("Test task started on the node {}", clusterService.localNode());
             if (request.shouldBlock) {
                 try {
-                    waitUntil(() -> {
+                    boolean unblocked = waitUntil(() -> {
                         if (((CancellableTask) task).isCancelled()) {
                             throw new RuntimeException("Cancelled!");
                         }
                         return ((TestTask) task).isBlocked() == false;
                     });
+                    assert unblocked : task + " hasn't been unblocked";
                 } catch (InterruptedException ex) {
                     Thread.currentThread().interrupt();
                 }