diff --git a/BasiliskII/src/Unix/posix_sem.cpp b/BasiliskII/src/Unix/posix_sem.cpp
index b0f3137c..3732d0e9 100644
--- a/BasiliskII/src/Unix/posix_sem.cpp
+++ b/BasiliskII/src/Unix/posix_sem.cpp
@@ -136,8 +136,8 @@ int sem_post(sem_t* sem)
 
 int sem_getvalue(sem_t* sem, int* sval)
 {
-	*sval = sem->sem_value;
-	return 0;
+	errno = ENOSYS;
+	return -1;
 }
 
 }