diff --git a/rxlib/src/main/java/org/rx/io/CompositeLock.java b/rxlib/src/main/java/org/rx/io/CompositeLock.java
index d087eebb..844558ab 100644
--- a/rxlib/src/main/java/org/rx/io/CompositeLock.java
+++ b/rxlib/src/main/java/org/rx/io/CompositeLock.java
@@ -34,26 +34,29 @@ enum Flags implements NEnum<Flags> {
 
     private final FileStream owner;
     private final FlagsEnum<Flags> flags;
-    final Map<FileStream.Block, ReadWriteLock> rwLocks = Collections.synchronizedMap(new ReferenceMap<>(AbstractReferenceMap.ReferenceStrength.HARD, AbstractReferenceMap.ReferenceStrength.WEAK));
+    final Map<FileStream.Block, ReadWriteLock> rwLocks = new ReferenceMap<>(AbstractReferenceMap.ReferenceStrength.HARD, AbstractReferenceMap.ReferenceStrength.WEAK);
 
     @SneakyThrows
     private <T> T lock(FileStream.Block block, boolean shared, @NonNull Func<T> fn) {
         Lock lock = null;
-        if (flags.has(Flags.READ_WRITE_LOCK)) {
-            ReadWriteLock rwLock = rwLocks.computeIfAbsent(block, k -> {
-                ReadWriteLock t = overlaps(k.position, k.size);
-                if (t == null) {
-                    t = new ReentrantReadWriteLock();
+        FileLock fLock = null;
+        try {
+            if (flags.has(Flags.READ_WRITE_LOCK)) {
+                ReadWriteLock rwLock;
+                synchronized (rwLocks) {
+                    rwLock = rwLocks.computeIfAbsent(block, k -> {
+                        ReadWriteLock t = overlaps(k.position, k.size);
+                        if (t == null) {
+                            t = new ReentrantReadWriteLock();
+                        }
+                        return t;
+                    });
                 }
-                return t;
-            });
 //            log.info("Lock {} - {}", rwLock, block);
-            lock = shared ? rwLock.readLock() : rwLock.writeLock();
-            lock.lock();
-        }
+                lock = shared ? rwLock.readLock() : rwLock.writeLock();
+                lock.lock();
+            }
 
-        FileLock fLock = null;
-        try {
             if (flags.has(Flags.FILE_LOCK)) {
                 fLock = owner.getRandomAccessFile().getChannel().lock(block.position, block.size, shared);
             }
diff --git a/rxlib/src/test/java/org/rx/io/TestIO.java b/rxlib/src/test/java/org/rx/io/TestIO.java
index 6789d34f..d942da99 100644
--- a/rxlib/src/test/java/org/rx/io/TestIO.java
+++ b/rxlib/src/test/java/org/rx/io/TestIO.java
@@ -5,6 +5,8 @@
 import lombok.Data;
 import lombok.SneakyThrows;
 import lombok.extern.slf4j.Slf4j;
+import org.apache.commons.collections4.map.AbstractReferenceMap;
+import org.apache.commons.collections4.map.ReferenceMap;
 import org.apache.commons.lang3.ClassUtils;
 import org.apache.commons.lang3.reflect.TypeUtils;
 import org.junit.jupiter.api.Test;
@@ -34,6 +36,8 @@
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
+import java.util.concurrent.locks.ReadWriteLock;
+import java.util.concurrent.locks.ReentrantReadWriteLock;
 
 import static org.rx.core.Extends.sleep;
 import static org.rx.core.Sys.toJsonString;
@@ -461,6 +465,33 @@ public void kvsIdx() {
         }, 100);
         log.info("{}", indexer);
     }
+
+    final Map<FileStream.Block, ReadWriteLock> rwLocks = Collections.synchronizedMap(new ReferenceMap<>(AbstractReferenceMap.ReferenceStrength.HARD, AbstractReferenceMap.ReferenceStrength.WEAK));
+
+    @Test
+    public void overlapsLock() {
+        ReentrantReadWriteLock r = new ReentrantReadWriteLock();
+        rwLocks.put(new FileStream.Block(4, 2), r);
+        assert overlaps(0, 4) == null;
+        assert overlaps(6, 10) == null;
+        assert overlaps(3, 1) == null;
+        assert overlaps(3, 2) == r;
+        assert overlaps(3, 4) == r;
+        assert overlaps(5, 1) == r;
+        assert overlaps(5, 3) == r;
+    }
+
+    private ReadWriteLock overlaps(long position, long size) {
+        for (Map.Entry<FileStream.Block, ReadWriteLock> entry : rwLocks.entrySet()) {
+            FileStream.Block block = entry.getKey();
+            if (position + size <= block.position)
+                continue;               // That is below this
+            if (block.position + block.size <= position)
+                continue;               // This is below that
+            return entry.getValue();
+        }
+        return null;
+    }
     //endregion
 
     @Test