Index: src/libcfa/concurrency/mutex.c
===================================================================
--- src/libcfa/concurrency/mutex.c	(revision 09800e9b5b749cee9e6635061d104d0b3b63c527)
+++ src/libcfa/concurrency/mutex.c	(revision 6c7099a9d37b5dcf81fe7ee2739fef0763b162e6)
@@ -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 )