diff --git a/classlib/src/main/java/org/teavm/classlib/java/lang/TThread.java b/classlib/src/main/java/org/teavm/classlib/java/lang/TThread.java
index b6bc09e6d..e8e58592a 100644
--- a/classlib/src/main/java/org/teavm/classlib/java/lang/TThread.java
+++ b/classlib/src/main/java/org/teavm/classlib/java/lang/TThread.java
@@ -38,6 +38,7 @@ public class TThread extends TObject implements TRunnable {
     private final Object finishedLock = new Object();
     private boolean interruptedFlag;
     public TThreadInterruptHandler interruptHandler;
+    public Object key;
 
     private String name;
     private boolean alive = true;
@@ -77,6 +78,7 @@ public class TThread extends TObject implements TRunnable {
         try {
             activeCount++;
             setCurrentThread(TThread.this);
+            key = new Object();
             TThread.this.run();
         } catch (Throwable t) {
             getUncaughtExceptionHandler().uncaughtException(this, t);
@@ -86,6 +88,7 @@ public class TThread extends TObject implements TRunnable {
             }
             alive = false;
             activeCount--;
+            key = null;
             setCurrentThread(mainThread);
         }
     }
diff --git a/classlib/src/main/java/org/teavm/classlib/java/lang/TThreadLocal.java b/classlib/src/main/java/org/teavm/classlib/java/lang/TThreadLocal.java
index 061f987a6..b3b02e7da 100644
--- a/classlib/src/main/java/org/teavm/classlib/java/lang/TThreadLocal.java
+++ b/classlib/src/main/java/org/teavm/classlib/java/lang/TThreadLocal.java
@@ -15,7 +15,12 @@
  */
 package org.teavm.classlib.java.lang;
 
+import java.util.Map;
+import java.util.WeakHashMap;
+import java.util.function.Supplier;
+
 public class TThreadLocal<T> extends TObject {
+    private Map<Object, Object> map;
     private boolean initialized;
     private T value;
 
@@ -27,21 +32,79 @@ public class TThreadLocal<T> extends TObject {
         return null;
     }
 
+    @SuppressWarnings("unchecked")
     public T get() {
-        if (!initialized) {
-            value = initialValue();
-            initialized = true;
+        if (isInMainThread()) {
+            if (!initialized) {
+                value = initialValue();
+                initialized = true;
+            }
+            cleanupMap();
+            return value;
+        } else {
+            var key = TThread.currentThread().key;
+            initMap();
+            var value = map.get(key);
+            if (value == null) {
+                value = initialValue();
+                map.put(key, value == null ? NULL : value);
+            } else if (value == NULL) {
+                value = null;
+            }
+            cleanupMap();
+            return (T) value;
         }
-        return value;
     }
 
     public void set(T value) {
-        initialized = true;
-        this.value = value;
+        if (isInMainThread()) {
+            initialized = true;
+            this.value = value;
+            cleanupMap();
+        } else {
+            initMap();
+            map.put(TThread.currentThread().key, value == null ? NULL : value);
+            cleanupMap();
+        }
     }
 
     public void remove() {
-        initialized = false;
-        value = null;
+        if (isInMainThread()) {
+            initialized = false;
+            value = null;
+            cleanupMap();
+        } else {
+            if (map != null) {
+                map.remove(TThread.currentThread().key);
+                cleanupMap();
+            }
+        }
     }
+
+    private void initMap() {
+        if (map == null) {
+            map = new WeakHashMap<>();
+        }
+    }
+
+    private void cleanupMap() {
+        if (map != null && map.isEmpty()) {
+            map = null;
+        }
+    }
+
+    public static <S> TThreadLocal<S> withInitial(Supplier<? extends S> supplier) {
+        return new TThreadLocal<>() {
+            @Override
+            protected S initialValue() {
+                return supplier.get();
+            }
+        };
+    }
+
+    private static boolean isInMainThread() {
+        return TThread.currentThread() == TThread.getMainThread();
+    }
+
+    private static final Object NULL = new Object();
 }
diff --git a/tests/src/test/java/org/teavm/classlib/java/lang/ThreadLocalTest.java b/tests/src/test/java/org/teavm/classlib/java/lang/ThreadLocalTest.java
new file mode 100644
index 000000000..06d1d3561
--- /dev/null
+++ b/tests/src/test/java/org/teavm/classlib/java/lang/ThreadLocalTest.java
@@ -0,0 +1,92 @@
+/*
+ *  Copyright 2024 Alexey Andreev.
+ *
+ *  Licensed 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.teavm.classlib.java.lang;
+
+import static org.junit.Assert.assertEquals;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.teavm.classlib.PlatformDetector;
+import org.teavm.interop.Async;
+import org.teavm.interop.AsyncCallback;
+import org.teavm.jso.browser.Window;
+import org.teavm.junit.OnlyPlatform;
+import org.teavm.junit.TeaVMTestRunner;
+import org.teavm.junit.TestPlatform;
+
+@RunWith(TeaVMTestRunner.class)
+public class ThreadLocalTest {
+    private volatile int counter;
+
+    @Test
+    @OnlyPlatform(TestPlatform.JAVASCRIPT)
+    public void concurrentUpdate() throws InterruptedException {
+        var local = new ThreadLocal<String>();
+        var monitor = new Object();
+        var results = new String[5];
+        counter = results.length;
+
+        for (var n = 0; n < results.length; ++n) {
+            var threadIndex = n;
+            new Thread(() -> {
+                var prefix = Character.toString((char) ('a' + threadIndex));
+                for (var i = 0; i < 10; ++i) {
+                    var old = local.get();
+                    if (old == null) {
+                        old = "";
+                    }
+                    local.set(old + prefix + i);
+                    sleep();
+                }
+                synchronized (monitor) {
+                    results[threadIndex] = local.get();
+                    --counter;
+                    monitor.notifyAll();
+                }
+            }).start();
+        }
+
+        do {
+            synchronized (monitor) {
+                monitor.wait();
+            }
+        } while (counter > 0);
+
+        assertEquals("a0a1a2a3a4a5a6a7a8a9", results[0]);
+        assertEquals("b0b1b2b3b4b5b6b7b8b9", results[1]);
+        assertEquals("c0c1c2c3c4c5c6c7c8c9", results[2]);
+        assertEquals("d0d1d2d3d4d5d6d7d8d9", results[3]);
+        assertEquals("e0e1e2e3e4e5e6e7e8e9", results[4]);
+    }
+
+    private void sleep() {
+        if (!PlatformDetector.isJavaScript()) {
+            try {
+                Thread.sleep(50);
+            } catch (InterruptedException e) {
+                throw new RuntimeException(e);
+            }
+        } else {
+            sleepInJs();
+        }
+    }
+
+    @Async
+    private static native void sleepInJs();
+
+    private static void sleepInJs(AsyncCallback<Void> callback) {
+        Window.setTimeout(() -> callback.complete(null), 0);
+    }
+}