diff --git a/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/DefaultAMSProcessor.java b/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/DefaultAMSProcessor.java
index 89fb3f7bd47c9e..313c0c609c8ffd 100644
--- a/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/DefaultAMSProcessor.java
+++ b/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/DefaultAMSProcessor.java
@@ -331,7 +331,9 @@ public void allocate(ApplicationAttemptId appAttemptId,
 
     response.setCompletedContainersStatuses(appAttempt
         .pullJustFinishedContainers());
-    response.setAvailableResources(allocation.getResourceLimit());
+    Resource resourceLimit = allocation.getResourceLimit();
+    response.setAvailableResources(resourceLimit == null ? null :
+        Resources.componentwiseMax(resourceLimit, Resources.none()));
 
     QueueMetrics queueMetrics =
         this.rmContext.getScheduler().getRootQueueMetrics();
diff --git a/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/test/java/org/apache/hadoop/yarn/server/resourcemanager/TestDefaultAMSProcessor.java b/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/test/java/org/apache/hadoop/yarn/server/resourcemanager/TestDefaultAMSProcessor.java
new file mode 100644
index 00000000000000..03dbb33161d007
--- /dev/null
+++ b/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/test/java/org/apache/hadoop/yarn/server/resourcemanager/TestDefaultAMSProcessor.java
@@ -0,0 +1,137 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.hadoop.yarn.server.resourcemanager;
+
+import org.apache.hadoop.yarn.api.protocolrecords.AllocateResponse;
+import org.apache.hadoop.yarn.api.records.ApplicationAttemptId;
+import org.apache.hadoop.yarn.api.records.ContainerId;
+import org.apache.hadoop.yarn.api.records.Resource;
+import org.apache.hadoop.yarn.conf.YarnConfiguration;
+import org.apache.hadoop.yarn.server.resourcemanager.rmapp.RMApp;
+import org.apache.hadoop.yarn.server.resourcemanager.scheduler.Allocation;
+import org.apache.hadoop.yarn.server.resourcemanager.scheduler.ContainerUpdates;
+import org.apache.hadoop.yarn.server.resourcemanager.scheduler.ResourceScheduler;
+import org.apache.hadoop.yarn.server.resourcemanager.scheduler.fifo.FifoScheduler;
+import org.apache.hadoop.yarn.api.records.ResourceRequest;
+import org.apache.hadoop.yarn.api.records.SchedulingRequest;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.Timeout;
+
+import java.util.List;
+
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+/**
+ * Tests for {@link DefaultAMSProcessor}.
+ */
+public class TestDefaultAMSProcessor {
+
+  /**
+   * Simulates transient YARN RM over-allocation by returning a negative
+   * resource limit from the scheduler.
+   */
+  public static class NegativeHeadroomScheduler extends FifoScheduler {
+    @Override
+    public Allocation allocate(ApplicationAttemptId applicationAttemptId,
+        List<ResourceRequest> ask,
+        List<SchedulingRequest> schedulingRequests,
+        List<ContainerId> release,
+        List<String> blacklistAdditions,
+        List<String> blacklistRemovals,
+        ContainerUpdates updateRequests) {
+      Allocation allocation = super.allocate(applicationAttemptId, ask,
+          schedulingRequests, release, blacklistAdditions,
+          blacklistRemovals, updateRequests);
+      allocation.setResourceLimit(Resource.newInstance(-1024, -4));
+      return allocation;
+    }
+  }
+
+  /**
+   * Simulates a scheduler that does not compute a resource limit,
+   * returning null from {@link Allocation#getResourceLimit()}.
+   */
+  public static class NullHeadroomScheduler extends FifoScheduler {
+    @Override
+    public Allocation allocate(ApplicationAttemptId applicationAttemptId,
+        List<ResourceRequest> ask,
+        List<SchedulingRequest> schedulingRequests,
+        List<ContainerId> release,
+        List<String> blacklistAdditions,
+        List<String> blacklistRemovals,
+        ContainerUpdates updateRequests) {
+      Allocation allocation = super.allocate(applicationAttemptId, ask,
+          schedulingRequests, release, blacklistAdditions,
+          blacklistRemovals, updateRequests);
+      allocation.setResourceLimit(null);
+      return allocation;
+    }
+  }
+
+  @Test
+  @Timeout(60)
+  public void testAvailableResourcesClampedToNonNegative() throws Exception {
+    YarnConfiguration conf = new YarnConfiguration();
+    conf.setClass(YarnConfiguration.RM_SCHEDULER,
+        NegativeHeadroomScheduler.class, ResourceScheduler.class);
+
+    MockRM rm = new MockRM(conf);
+    rm.start();
+    MockNM nm = rm.registerNode("127.0.0.1:1234", 8 * 1024, 8);
+
+    RMApp app = MockRMAppSubmitter.submitWithMemory(1024, rm);
+    MockAM am = MockRM.launchAndRegisterAM(app, rm, nm);
+
+    AllocateResponse response = am.doHeartbeat();
+    Resource available = response.getAvailableResources();
+
+    assertTrue(available.getMemorySize() >= 0,
+        "Available memory must be non-negative, but was: "
+            + available.getMemorySize());
+    assertTrue(available.getVirtualCores() >= 0,
+        "Available vCores must be non-negative, but was: "
+            + available.getVirtualCores());
+
+    rm.stop();
+  }
+
+  @Test
+  @Timeout(60)
+  public void testNullResourceLimitDoesNotThrow() throws Exception {
+    YarnConfiguration conf = new YarnConfiguration();
+    conf.setClass(YarnConfiguration.RM_SCHEDULER,
+        NullHeadroomScheduler.class, ResourceScheduler.class);
+
+    MockRM rm = new MockRM(conf);
+    rm.start();
+    MockNM nm = rm.registerNode("127.0.0.1:1234", 8 * 1024, 8);
+
+    RMApp app = MockRMAppSubmitter.submitWithMemory(1024, rm);
+    MockAM am = MockRM.launchAndRegisterAM(app, rm, nm);
+
+    AllocateResponse response = am.doHeartbeat();
+
+    assertNull(response.getAvailableResources(),
+        "Available resources must remain null when the scheduler "
+            + "returns a null resource limit");
+
+    rm.stop();
+  }
+}