diff --git oak-segment-tar/src/test/java/org/apache/jackrabbit/oak/segment/CompactionAndCleanupIT.java oak-segment-tar/src/test/java/org/apache/jackrabbit/oak/segment/CompactionAndCleanupIT.java
index 42ade59..ea3c38a 100644
--- oak-segment-tar/src/test/java/org/apache/jackrabbit/oak/segment/CompactionAndCleanupIT.java
+++ oak-segment-tar/src/test/java/org/apache/jackrabbit/oak/segment/CompactionAndCleanupIT.java
@@ -25,8 +25,8 @@ import static java.lang.Integer.getInteger;
 import static java.util.concurrent.TimeUnit.SECONDS;
 import static org.apache.commons.io.FileUtils.byteCountToDisplaySize;
 import static org.apache.jackrabbit.oak.api.Type.STRING;
-import static org.apache.jackrabbit.oak.commons.FixturesHelper.Fixture.SEGMENT_MK;
 import static org.apache.jackrabbit.oak.commons.FixturesHelper.getFixtures;
+import static org.apache.jackrabbit.oak.commons.FixturesHelper.Fixture.SEGMENT_MK;
 import static org.apache.jackrabbit.oak.plugins.memory.EmptyNodeState.EMPTY_NODE;
 import static org.apache.jackrabbit.oak.segment.compaction.SegmentGCOptions.defaultGCOptions;
 import static org.apache.jackrabbit.oak.segment.file.FileStoreBuilder.fileStoreBuilder;
@@ -46,32 +46,38 @@ import java.util.Set;
 import java.util.UUID;
 import java.util.concurrent.Callable;
 import java.util.concurrent.ExecutionException;
+import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.FutureTask;
 import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicReference;
 
-import com.google.common.io.ByteStreams;
 import org.apache.jackrabbit.oak.api.Blob;
 import org.apache.jackrabbit.oak.api.CommitFailedException;
 import org.apache.jackrabbit.oak.api.PropertyState;
 import org.apache.jackrabbit.oak.api.Type;
+import org.apache.jackrabbit.oak.commons.concurrent.ExecutorCloser;
 import org.apache.jackrabbit.oak.segment.compaction.SegmentGCOptions;
 import org.apache.jackrabbit.oak.segment.file.FileStore;
+import org.apache.jackrabbit.oak.segment.file.FileStoreGCMonitor;
 import org.apache.jackrabbit.oak.spi.commit.CommitInfo;
 import org.apache.jackrabbit.oak.spi.commit.EmptyHook;
 import org.apache.jackrabbit.oak.spi.state.ChildNodeEntry;
 import org.apache.jackrabbit.oak.spi.state.NodeBuilder;
 import org.apache.jackrabbit.oak.spi.state.NodeState;
 import org.apache.jackrabbit.oak.spi.state.NodeStore;
+import org.apache.jackrabbit.oak.stats.Clock;
 import org.apache.jackrabbit.oak.stats.DefaultStatisticsProvider;
+import org.apache.jackrabbit.oak.stats.StatisticsProvider;
 import org.junit.Rule;
 import org.junit.Test;
 import org.junit.rules.TemporaryFolder;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import com.google.common.io.ByteStreams;
+
 public class CompactionAndCleanupIT {
 
     private static final Logger log = LoggerFactory
@@ -924,6 +930,56 @@ public class CompactionAndCleanupIT {
             fileStore.close();
         }
     }
+    
+    /**
+     * Test asserting OAK-4106 : Concurrent writes during cleanup should not
+     * impact reclaimedSize computation.
+     */
+    @Test
+    public void concurrentWritesDuringCleanup() throws Exception {
+        ScheduledExecutorService executor = Executors.newSingleThreadScheduledExecutor();
+        StatisticsProvider statsProvider = new DefaultStatisticsProvider(executor);
+        final FileStoreGCMonitor fileStoreGCMonitor = new FileStoreGCMonitor(Clock.SIMPLE);
+        
+        final FileStore fileStore = fileStoreBuilder(getFileStoreFolder())
+                .withGCOptions(defaultGCOptions().setRetainedGenerations(2))
+                .withGCMonitor(fileStoreGCMonitor)
+                .withStatisticsProvider(statsProvider)
+                .withMaxFileSize(1)
+                .build();
+        
+        final SegmentNodeStore nodeStore = SegmentNodeStoreBuilders.builder(fileStore).build();
+
+        try {
+            Runnable concurrentWriteTask = new Runnable() {
+                public void run() {
+                    try {
+                        NodeBuilder builder = nodeStore.getRoot().builder();
+                        builder.setProperty("blob" + new Random().nextInt(), createBlob(nodeStore, 256 * 256));
+
+                        nodeStore.merge(builder, EmptyHook.INSTANCE, CommitInfo.EMPTY);
+                        fileStore.flush();
+                    } catch (CommitFailedException e) {
+                        // ignore
+                    } catch (IOException e) {
+                        // ignore
+                    }
+                };
+            };
+            
+            ExecutorService executorService = Executors.newFixedThreadPool(5);
+            for (int i = 0; i < 5; i++) {
+                executorService.execute(concurrentWriteTask);
+            }
+
+            fileStore.cleanup();
+            assertTrue(fileStoreGCMonitor.getLastReclaimedSize() == 0);
+            
+            new ExecutorCloser(executorService).close();
+        } finally {
+            fileStore.close();
+        }
+    }
 
     private static void addContent(NodeBuilder builder) {
         for (int k = 0; k < 10000; k++) {