diff --git a/src/os/unix/ngx_thread.h b/src/os/unix/ngx_thread.h
index ce305de..9637fda 100644
--- a/src/os/unix/ngx_thread.h
+++ b/src/os/unix/ngx_thread.h
@@ -28,7 +28,7 @@
 
 #define NGX_MUTEX_LOCK_BUSY  0x80000000
 
-typedef struct {
+typedef volatile struct {
     ngx_atomic_t  lock;
     ngx_log_t    *log;
     int           semid;