diff --git a/src/buffer.h b/src/buffer.h
index bc74d7a..8988d12 100644
--- a/src/buffer.h
+++ b/src/buffer.h
@@ -14,7 +14,7 @@ struct MemoryStack {
     int totalAllocated;
     int totalFreed;
 #ifdef ZTS
-    tsrm_mutex_t lock;
+    MUTEX_T lock;
 #endif
 };