diff --git a/repos/libports/src/lib/pthread/thread.cc b/repos/libports/src/lib/pthread/thread.cc
index f918894e91..c086008170 100644
--- a/repos/libports/src/lib/pthread/thread.cc
+++ b/repos/libports/src/lib/pthread/thread.cc
@@ -57,6 +57,53 @@ static __attribute__((constructor)) Thread * main_thread()
 }
 
 
+void Pthread_registry::insert(pthread_t thread)
+{
+	/* prevent multiple insertions at the same location */
+	static Genode::Lock insert_lock;
+	Genode::Lock::Guard insert_lock_guard(insert_lock);
+
+	for (unsigned int i = 0; i < MAX_NUM_PTHREADS; i++) {
+		if (_array[i] == 0) {
+			_array[i] = thread;
+			return;
+		}
+	}
+
+	Genode::error("pthread registry overflow, pthread_self() might fail");
+}
+
+
+void Pthread_registry::remove(pthread_t thread)
+{
+	for (unsigned int i = 0; i < MAX_NUM_PTHREADS; i++) {
+		if (_array[i] == thread) {
+			_array[i] = 0;
+			return;
+		}
+	}
+
+	Genode::error("could not remove unknown pthread from registry");
+}
+
+
+bool Pthread_registry::contains(pthread_t thread)
+{
+	for (unsigned int i = 0; i < MAX_NUM_PTHREADS; i++)
+		if (_array[i] == thread)
+			return true;
+
+	return false;
+}
+
+
+Pthread_registry &pthread_registry()
+{
+	static Pthread_registry instance;
+	return instance;
+}
+
+
 extern "C" {
 
 	/* Thread */
@@ -129,9 +176,10 @@ extern "C" {
 	{
 		Thread *myself = Thread::myself();
 
-		pthread_t pthread = dynamic_cast<pthread_t>(myself);
-		if (pthread)
-			return pthread;
+		pthread_t pthread_myself = static_cast<pthread_t>(myself);
+
+		if (pthread_registry().contains(pthread_myself))
+			return pthread_myself;
 
 		/*
 		 * We pass here if the main thread or an alien thread calls
diff --git a/repos/libports/src/lib/pthread/thread.h b/repos/libports/src/lib/pthread/thread.h
index f7a7741e74..4189197adc 100644
--- a/repos/libports/src/lib/pthread/thread.h
+++ b/repos/libports/src/lib/pthread/thread.h
@@ -18,6 +18,31 @@
 
 #include <pthread.h>
 
+/*
+ * Used by 'pthread_self()' to find out if the current thread is an alien
+ * thread.
+ */
+class Pthread_registry
+{
+	private:
+
+		enum { MAX_NUM_PTHREADS = 128 };
+
+		pthread_t _array[MAX_NUM_PTHREADS] = { 0 };
+
+	public:
+
+		void insert(pthread_t thread);
+
+		void remove(pthread_t thread);
+
+		bool contains(pthread_t thread);
+};
+
+
+Pthread_registry &pthread_registry();
+
+
 extern "C" {
 
 	struct pthread_attr
@@ -50,6 +75,8 @@ extern "C" {
 		{
 			if (_attr)
 				_attr->pthread = this;
+
+			pthread_registry().insert(this);
 		}
 
 		/**
@@ -62,6 +89,13 @@ extern "C" {
 		{
 			if (_attr)
 				_attr->pthread = this;
+
+			pthread_registry().insert(this);
+		}
+
+		virtual ~pthread()
+		{
+			pthread_registry().remove(this);
 		}
 
 		void entry()