Index: src/libcfa/concurrency/mutex.c
===================================================================
--- src/libcfa/concurrency/mutex.c	(revision 09800e9b5b749cee9e6635061d104d0b3b63c527)
+++ src/libcfa/concurrency/mutex.c	(revision 0c674e80fb16ad200b53123b9c7451e3a60db3ae)
@@ -59,5 +59,5 @@
 void unlock(mutex_lock & this) {
 	lock( this.lock __cfaabi_dbg_ctx2 );
-	this.is_locked = this.blocked_threads;
+	this.is_locked = (this.blocked_threads != 0);
 	WakeThread(
 		pop_head( this.blocked_threads )