diff --git a/winsup/cygwin/ChangeLog b/winsup/cygwin/ChangeLog
index efbaffb9f..022a25103 100644
--- a/winsup/cygwin/ChangeLog
+++ b/winsup/cygwin/ChangeLog
@@ -1,3 +1,12 @@
+2009-01-20  Corinna Vinschen  <corinna@vinschen.de>
+
+	* thread.h (struct pthread_rwlock::RWLOCK_READER): Add counter n.
+	* thread.cc (pthread_rwlock::rdlock): If a thread already owns a
+	read lock, just count the number of locks for it, per SUSv4.
+	(pthread_rwlock::tryrdlock): Ditto.
+	(pthread_rwlock::unlock): If a thread has more than one concurrent
+	read locks, just count down.
+
 2009-01-20  Corinna Vinschen  <corinna@vinschen.de>
 
 	* autoload.cc (WSAIoctl): Reintroduce.
diff --git a/winsup/cygwin/thread.cc b/winsup/cygwin/thread.cc
index ecf928784..8bb68703e 100644
--- a/winsup/cygwin/thread.cc
+++ b/winsup/cygwin/thread.cc
@@ -1227,9 +1227,13 @@ pthread_rwlock::rdlock ()
 
   mtx.lock ();
 
-  if (lookup_reader (self))
+  reader = lookup_reader (self);
+  if (reader)
     {
-      result = EDEADLK;
+      if (reader->n < ULONG_MAX)
+	++reader->n;
+      else
+      	errno = EAGAIN;
       goto DONE;
     }
 
@@ -1252,6 +1256,7 @@ pthread_rwlock::rdlock ()
     }
 
   reader->thread = self;
+  reader->n = 1;
   add_reader (reader);
 
  DONE:
@@ -1272,10 +1277,15 @@ pthread_rwlock::tryrdlock ()
     result = EBUSY;
   else
     {
-      struct RWLOCK_READER *reader = new struct RWLOCK_READER;
-      if (reader)
+      struct RWLOCK_READER *reader;
+
+      reader = lookup_reader (self);
+      if (reader && reader->n < ULONG_MAX)
+	++reader->n;
+      else if ((reader = new struct RWLOCK_READER))
 	{
 	  reader->thread = self;
+	  reader->n = 1;
 	  add_reader (reader);
 	}
       else
@@ -1365,6 +1375,8 @@ pthread_rwlock::unlock ()
 	  result = EPERM;
 	  goto DONE;
 	}
+      if (--reader->n > 0)
+      	goto DONE;
 
       remove_reader (reader);
       delete reader;
diff --git a/winsup/cygwin/thread.h b/winsup/cygwin/thread.h
index db94fd2c2..c2a1be8f1 100644
--- a/winsup/cygwin/thread.h
+++ b/winsup/cygwin/thread.h
@@ -556,6 +556,7 @@ public:
   {
     struct RWLOCK_READER *next;
     pthread_t thread;
+    unsigned long n;
   } *readers;
   fast_mutex readers_mx;