diff --git a/libjava/ChangeLog b/libjava/ChangeLog
index 356b3ba0ab7..ba83c06cf2e 100644
--- a/libjava/ChangeLog
+++ b/libjava/ChangeLog
@@ -1,3 +1,13 @@
+2005-06-29  Tom Tromey  <tromey@redhat.com>
+
+	PR libgcj/22211:
+	* testsuite/libjava.lang/pr22211.java: New file.
+	* java/lang/natThread.cc (finish_): Synchronize when updating
+	alive_flag.
+	(_Jv_AttachCurrentThread): Likewise.
+	(interrupt): Only call _Jv_ThreadInterrupt if thread is alive.
+	* java/lang/Thread.java (isAlive): Now synchronized.
+
 2005-06-29  Tom Tromey  <tromey@redhat.com>
 
 	* interpret.cc (run) <insn_checkcast, checkcast_resolved>: Use
diff --git a/libjava/java/lang/Thread.java b/libjava/java/lang/Thread.java
index ef4a3f472f0..b58ff175c02 100644
--- a/libjava/java/lang/Thread.java
+++ b/libjava/java/lang/Thread.java
@@ -550,7 +550,7 @@ public class Thread implements Runnable
    *
    * @return whether this Thread is alive
    */
-  public final boolean isAlive()
+  public final synchronized boolean isAlive()
   {
     return alive_flag;
   }
diff --git a/libjava/java/lang/natThread.cc b/libjava/java/lang/natThread.cc
index e79ab11b9c6..f1064f17c69 100644
--- a/libjava/java/lang/natThread.cc
+++ b/libjava/java/lang/natThread.cc
@@ -1,6 +1,6 @@
 // natThread.cc - Native part of Thread class.
 
-/* Copyright (C) 1998, 1999, 2000, 2001, 2002  Free Software Foundation
+/* Copyright (C) 1998, 1999, 2000, 2001, 2002, 2005  Free Software Foundation
 
    This file is part of libgcj.
 
@@ -115,7 +115,9 @@ java::lang::Thread::interrupt (void)
 {
   checkAccess ();
   natThread *nt = (natThread *) data;
-  _Jv_ThreadInterrupt (nt->thread);
+  JvSynchronize sync (this);
+  if (alive_flag)
+    _Jv_ThreadInterrupt (nt->thread);
 }
 
 void
@@ -215,7 +217,12 @@ java::lang::Thread::finish_ ()
   
   // Signal any threads that are waiting to join() us.
   _Jv_MutexLock (&nt->join_mutex);
-  alive_flag = false;
+
+  {
+    JvSynchronize sync (this);
+    alive_flag = false;
+  }
+
   _Jv_CondNotifyAll (&nt->join_cond, &nt->join_mutex);
   _Jv_MutexUnlock (&nt->join_mutex);  
 }
@@ -392,6 +399,7 @@ _Jv_SetCurrentJNIEnv (JNIEnv *env)
 jint
 _Jv_AttachCurrentThread(java::lang::Thread* thread)
 {
+  JvSynchronize sync (thread);
   if (thread == NULL || thread->startable_flag == false)
     return -1;
   thread->startable_flag = false;
diff --git a/libjava/testsuite/libjava.lang/pr22211.java b/libjava/testsuite/libjava.lang/pr22211.java
new file mode 100644
index 00000000000..87a8e555c5d
--- /dev/null
+++ b/libjava/testsuite/libjava.lang/pr22211.java
@@ -0,0 +1,8 @@
+public class pr22211
+{
+  public static void main(String[] args)
+  {
+    Thread x = new Thread();
+    x.interrupt();
+  }
+}