diff --git a/CHANGES.txt b/CHANGES.txt
index 587ca0e973..c3dfe1b04b 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -6,6 +6,7 @@
  * Allow nodetool garbagecollect to take a user defined list of SSTables (CASSANDRA-16767)
  * Add a guardrail for misprepared statements (CASSANDRA-21139)
 Merged from 6.0:
+ * Fix operationMode reporting DECOMMISSION_FAILED instead of LEAVING when resuming a failed decommission (CASSANDRA-21493)
  * Avoid megamorphic calls when serializing and deserializing fixed-length values (CASSANDRA-21536)
  * Avoid megamorphic calls for Cell.timestamp/ttl/path/localDeletionTimeAsUnsignedInt methods (CASSANDRA-21526)
  * Reduce allocations in DefaultQueryOptions (CASSANDRA-21467)
diff --git a/src/java/org/apache/cassandra/tcm/sequences/SingleNodeSequences.java b/src/java/org/apache/cassandra/tcm/sequences/SingleNodeSequences.java
index 313700aaaf..82a1059b6e 100644
--- a/src/java/org/apache/cassandra/tcm/sequences/SingleNodeSequences.java
+++ b/src/java/org/apache/cassandra/tcm/sequences/SingleNodeSequences.java
@@ -92,6 +92,7 @@ public interface SingleNodeSequences
         else if (InProgressSequences.isLeave(inProgress))
         {
             logger.info("Resuming decommission @ {} (current epoch = {}): {}", inProgress.latestModification, metadata.epoch, inProgress.status());
+            StorageService.instance.clearTransientMode();
         }
         else
         {
diff --git a/test/distributed/org/apache/cassandra/distributed/test/DecommissionTest.java b/test/distributed/org/apache/cassandra/distributed/test/DecommissionTest.java
index ad0120513b..41f8274ae5 100644
--- a/test/distributed/org/apache/cassandra/distributed/test/DecommissionTest.java
+++ b/test/distributed/org/apache/cassandra/distributed/test/DecommissionTest.java
@@ -21,6 +21,7 @@ package org.apache.cassandra.distributed.test;
 import java.io.IOException;
 import java.util.concurrent.Callable;
 import java.util.concurrent.ExecutionException;
+import java.util.concurrent.atomic.AtomicBoolean;
 
 import net.bytebuddy.ByteBuddy;
 import net.bytebuddy.dynamic.loading.ClassLoadingStrategy;
@@ -141,6 +142,7 @@ public class DecommissionTest extends TestBaseImpl
 
     public static class BB
     {
+        static final AtomicBoolean injected = new AtomicBoolean(false);
         public static void install(ClassLoader classLoader, Integer num)
         {
             if (num == 2)
@@ -157,7 +159,7 @@ public class DecommissionTest extends TestBaseImpl
         public static void execute(NodeId leaving, PlacementDeltas startLeave, PlacementDeltas midLeave, PlacementDeltas finishLeave,
                                    @SuperCall Callable<?> zuper) throws ExecutionException, InterruptedException
         {
-            if (!StorageService.instance.isDecommissionFailed())
+            if (injected.compareAndSet(false, true))
                 throw new ExecutionException(new RuntimeException("simulated error in prepareUnbootstrapStreaming"));
 
             try
diff --git a/test/distributed/org/apache/cassandra/distributed/test/ring/DecommissionTest.java b/test/distributed/org/apache/cassandra/distributed/test/ring/DecommissionTest.java
index 307956828e..f6ba5c33a1 100644
--- a/test/distributed/org/apache/cassandra/distributed/test/ring/DecommissionTest.java
+++ b/test/distributed/org/apache/cassandra/distributed/test/ring/DecommissionTest.java
@@ -53,8 +53,10 @@ import org.apache.cassandra.service.StorageService;
 import org.apache.cassandra.streaming.StreamSession;
 import org.apache.cassandra.tcm.ClusterMetadata;
 import org.apache.cassandra.tcm.ClusterMetadataService;
+import org.apache.cassandra.tcm.Epoch;
 import org.apache.cassandra.tcm.membership.NodeId;
 import org.apache.cassandra.tcm.membership.NodeVersion;
+import org.apache.cassandra.tcm.transformations.PrepareLeave;
 import org.apache.cassandra.tcm.transformations.Startup;
 import org.apache.cassandra.utils.CassandraVersion;
 import org.apache.cassandra.utils.FBUtilities;
@@ -62,6 +64,8 @@ import org.apache.cassandra.utils.FBUtilities;
 import static net.bytebuddy.matcher.ElementMatchers.named;
 import static org.apache.cassandra.distributed.api.Feature.GOSSIP;
 import static org.apache.cassandra.distributed.api.Feature.NETWORK;
+import static org.apache.cassandra.distributed.shared.ClusterUtils.pauseBeforeCommit;
+import static org.apache.cassandra.distributed.shared.ClusterUtils.unpauseCommits;
 import static org.apache.cassandra.distributed.shared.NetworkTopology.dcAndRack;
 import static org.apache.cassandra.distributed.shared.NetworkTopology.networkTopology;
 import static org.apache.cassandra.distributed.test.ring.BootstrapTest.populate;
@@ -84,6 +88,43 @@ public class DecommissionTest extends TestBaseImpl
         }
     }
 
+    @Test
+    public void testOperationModeOnDecomResume() throws Exception
+    {
+        // Node 2's first decomission attempt fails mid-stream (injected by BB), leaving it in
+        // DECOMISSION_FAILED. On resume, operationMode() must transition back to LEAVING before
+        // MID_LEAVE is committed. We pause the CMS just before that commit to assert the mode
+        // in the window where streaming has finished but the epoch has not yet advanced.
+        try (Cluster cluster = builder().withNodes(3)
+                                        .withConfig(config -> config.with(NETWORK, GOSSIP))
+                                        .withInstanceInitializer(BB::install)
+                                        .start())
+        {
+            populate(cluster, 0, 100, 1, 2, ConsistencyLevel.QUORUM);
+
+            IInvokableInstance cmsNode = cluster.get(1);
+            IInvokableInstance leavingNode = cluster.get(2);
+
+            // --force required: cie_internal keyspace has RF=3, decommission would fail replication check otherwise
+            leavingNode.nodetoolResult("decommission", "--force").asserts().failure();
+            leavingNode.runOnInstance(() -> assertEquals(StorageService.Mode.DECOMMISSION_FAILED, StorageService.instance.operationMode()));
+
+            Callable<Epoch> midLeavePaused = pauseBeforeCommit(cmsNode, e -> e instanceof PrepareLeave.MidLeave);
+
+            Thread resumeThread = new Thread(() -> leavingNode.nodetoolResult("decommission").asserts().success());
+            resumeThread.start();
+            midLeavePaused.call();
+
+            leavingNode.runOnInstance(() ->
+                assertEquals("operationMode during resumed decommission streaming should be LEAVING, not DECOMMISSION_FAILED",
+                             StorageService.Mode.LEAVING,
+                             StorageService.instance.operationMode()));
+
+            unpauseCommits(cmsNode);
+            resumeThread.join(TimeUnit.MINUTES.toMillis(2));
+        }
+    }
+
     @Test
     public void testAddressReuseAfterDecommission() throws IOException, ExecutionException, InterruptedException
     {