diff --git a/include/drmhwcgralloc.h b/include/drmhwcgralloc.h
index 57685d1..09c7499 100644
--- a/include/drmhwcgralloc.h
+++ b/include/drmhwcgralloc.h
@@ -28,6 +28,8 @@
   uint32_t usage;
   uint32_t pitches[HWC_DRM_BO_MAX_PLANES];
   uint32_t offsets[HWC_DRM_BO_MAX_PLANES];
+  /* sizes[] is used only by mapper@4 metadata getter for internal purposes */
+  uint32_t sizes[HWC_DRM_BO_MAX_PLANES];
   int prime_fds[HWC_DRM_BO_MAX_PLANES];
   uint64_t modifiers[HWC_DRM_BO_MAX_PLANES];
   int acquire_fence_fd;