diff --git a/hadoop-yarn-project/CHANGES.txt b/hadoop-yarn-project/CHANGES.txt
index 1a19f52803..99b900672e 100644
--- a/hadoop-yarn-project/CHANGES.txt
+++ b/hadoop-yarn-project/CHANGES.txt
@@ -239,6 +239,9 @@ Release 2.5.0 - UNRELEASED
     YARN-2075. Fixed the test failure of TestRMAdminCLI. (Kenji Kikushima via
     zjshen)
 
+    YARN-2155. FairScheduler: Incorrect threshold check for preemption.
+    (Wei Yan via kasha)
+
 Release 2.4.1 - UNRELEASED
 
   INCOMPATIBLE CHANGES
diff --git a/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/fair/FairScheduler.java b/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/fair/FairScheduler.java
index 5725f8c383..ea53165c63 100644
--- a/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/fair/FairScheduler.java
+++ b/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/fair/FairScheduler.java
@@ -1072,8 +1072,8 @@ private void updateRootQueueMetrics() {
   private boolean shouldAttemptPreemption() {
     if (preemptionEnabled) {
       return (preemptionUtilizationThreshold < Math.max(
-          (float) rootMetrics.getAvailableMB() / clusterResource.getMemory(),
-          (float) rootMetrics.getAvailableVirtualCores() /
+          (float) rootMetrics.getAllocatedMB() / clusterResource.getMemory(),
+          (float) rootMetrics.getAllocatedVirtualCores() /
               clusterResource.getVirtualCores()));
     }
     return false;
diff --git a/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/test/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/fair/TestFairSchedulerPreemption.java b/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/test/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/fair/TestFairSchedulerPreemption.java
index 2098e1679b..310104bd08 100644
--- a/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/test/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/fair/TestFairSchedulerPreemption.java
+++ b/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/test/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/fair/TestFairSchedulerPreemption.java
@@ -146,7 +146,7 @@ public void testPreemptionWithFreeResources() throws Exception {
     // Create node with 4GB memory and 4 vcores
     registerNodeAndSubmitApp(4 * 1024, 4, 2, 1024);
 
-    // Verify submitting another request doesn't trigger preemption
+    // Verify submitting another request triggers preemption
     createSchedulingRequest(1024, "queueB", "user1", 1, 1);
     scheduler.update();
     clock.tick(6);
@@ -171,5 +171,21 @@ public void testPreemptionWithFreeResources() throws Exception {
     scheduler.preemptTasksIfNecessary();
     assertEquals("preemptResources() should not have been called", -1,
         ((StubbedFairScheduler) scheduler).lastPreemptMemory);
+
+    resourceManager.stop();
+
+    startResourceManager(0.7f);
+    // Create node with 4GB memory and 4 vcores
+    registerNodeAndSubmitApp(4 * 1024, 4, 3, 1024);
+
+    // Verify submitting another request triggers preemption
+    createSchedulingRequest(1024, "queueB", "user1", 1, 1);
+    scheduler.update();
+    clock.tick(6);
+
+    ((StubbedFairScheduler) scheduler).resetLastPreemptResources();
+    scheduler.preemptTasksIfNecessary();
+    assertEquals("preemptResources() should have been called", 1024,
+        ((StubbedFairScheduler) scheduler).lastPreemptMemory);
   }
 }