diff --git a/src/d3d9/d3d9_common_buffer.h b/src/d3d9/d3d9_common_buffer.h
index 8ddb0d61..782be427 100644
--- a/src/d3d9/d3d9_common_buffer.h
+++ b/src/d3d9/d3d9_common_buffer.h
@@ -225,7 +225,7 @@ namespace dxvk {
 
     D3D9DeviceEx*               m_parent;
     const D3D9_BUFFER_DESC      m_desc;
-    DWORD                       m_mapFlags;
+    DWORD                       m_mapFlags = 0;
     bool                        m_needsReadback = false;
     D3D9_COMMON_BUFFER_MAP_MODE m_mapMode;