diff --git a/pistachio/include/read_write_lock.h b/pistachio/include/read_write_lock.h
index d667451..49f7f30 100644
--- a/pistachio/include/read_write_lock.h
+++ b/pistachio/include/read_write_lock.h
@@ -123,7 +123,7 @@ struct read_write_lock_t
     bool is_locked(void);
 
 #if defined(CONFIG_DEBUG)
-    word_t locked;
+    word_t volatile locked;
 #endif
 };