diff --git a/flink-tests/src/test/java/org/apache/flink/test/checkpointing/UnalignedCheckpointITCase.java b/flink-tests/src/test/java/org/apache/flink/test/checkpointing/UnalignedCheckpointITCase.java
index effbbc52fc81d..f649b8f7df378 100644
--- a/flink-tests/src/test/java/org/apache/flink/test/checkpointing/UnalignedCheckpointITCase.java
+++ b/flink-tests/src/test/java/org/apache/flink/test/checkpointing/UnalignedCheckpointITCase.java
@@ -38,12 +38,10 @@
 import org.apache.flink.streaming.api.datastream.SingleOutputStreamOperator;
 import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;
 import org.apache.flink.streaming.api.functions.KeyedProcessFunction;
-import org.apache.flink.testutils.junit.FailsWithAdaptiveScheduler;
 import org.apache.flink.util.Collector;
 
 import org.apache.commons.lang3.ArrayUtils;
 import org.junit.Test;
-import org.junit.experimental.categories.Category;
 import org.junit.runner.RunWith;
 import org.junit.runners.Parameterized;
 
@@ -105,7 +103,6 @@
  * </ul>
  */
 @RunWith(Parameterized.class)
-@Category(FailsWithAdaptiveScheduler.class) // FLINK-21689
 public class UnalignedCheckpointITCase extends UnalignedCheckpointTestBase {
     enum Topology implements DagCreator {
         PIPELINE {
diff --git a/flink-tests/src/test/java/org/apache/flink/test/checkpointing/UnalignedCheckpointTestBase.java b/flink-tests/src/test/java/org/apache/flink/test/checkpointing/UnalignedCheckpointTestBase.java
index c6201faff07cd..25eef0480b1c1 100644
--- a/flink-tests/src/test/java/org/apache/flink/test/checkpointing/UnalignedCheckpointTestBase.java
+++ b/flink-tests/src/test/java/org/apache/flink/test/checkpointing/UnalignedCheckpointTestBase.java
@@ -104,8 +104,16 @@
 import static org.apache.flink.streaming.api.environment.ExecutionCheckpointingOptions.CHECKPOINTING_TIMEOUT;
 import static org.apache.flink.util.Preconditions.checkState;
 
-/** Base class for tests related to unaligned checkpoints. */
-@Category(FailsWithAdaptiveScheduler.class) // FLINK-21689
+/**
+ * Base class for tests related to unaligned checkpoints.
+ *
+ * <p>This test base relies on restarting the subtasks within the scheduler to trigger a reset of
+ * the operators. The operator reset is counted in the LongSource. The job will terminate if the
+ * number of expected restarts is reached. The AdaptiveScheduler won't trigger the operator reset
+ * resulting in the test running forever. This is why this test suite is disabled for the {@link
+ * org.apache.flink.runtime.scheduler.adaptive.AdaptiveScheduler}.
+ */
+@Category(FailsWithAdaptiveScheduler.class)
 public abstract class UnalignedCheckpointTestBase extends TestLogger {
     protected static final Logger LOG = LoggerFactory.getLogger(UnalignedCheckpointTestBase.class);
     protected static final String NUM_INPUTS = "inputs_";