```diff
diff --git a/core/src/main/java/org/jruby/ext/jruby/JRubyUtilLibrary.java b/core/src/main/java/org/jruby/ext/jruby/JRubyUtilLibrary.java
index 327f29f353..ecf979d564 100644
--- a/core/src/main/java/org/jruby/ext/jruby/JRubyUtilLibrary.java
+++ b/core/src/main/java/org/jruby/ext/jruby/JRubyUtilLibrary.java
@@ -39,6 +39,7 @@ import org.jruby.anno.JRubyMethod;
 import org.jruby.ast.util.ArgsUtil;
 import org.jruby.exceptions.RaiseException;
 import org.jruby.javasupport.Java;
+import org.jruby.runtime.Block;
 import org.jruby.runtime.ThreadContext;
 import org.jruby.runtime.builtin.IRubyObject;
 import org.jruby.runtime.load.BasicLibraryService;
@@ -248,6 +249,22 @@ public class JRubyUtilLibrary implements Library {
         }
     }
 
+    /**
+     * Invoke the given block under synchronized lock, using standard Java synchronization.
+     *
+     * @param context the current context
+     * @param recv the JRuby module
+     * @param arg the object against which to synchronize
+     * @param block the block to execute
+     * @return the return value of the block
+     */
+    @JRubyMethod(name = "synchronized")
+    public static IRubyObject rbSynchronized(ThreadContext context, IRubyObject recv, IRubyObject arg, Block block) {
+        synchronized (arg) {
+            return block.call(context);
+        }
+    }
+
     @Deprecated // since 9.2 only loaded with require 'core_ext/string.rb'
     public static class StringUtils {
         public static IRubyObject unseeded_hash(ThreadContext context, IRubyObject recv) {

```