diff --git a/include/drm/drm.h b/include/drm/drm.h
index 616824be..71a2ac10 100644
--- a/include/drm/drm.h
+++ b/include/drm/drm.h
@@ -780,6 +780,7 @@ struct drm_event_vblank {
 #define DRM_CAP_DUMB_PREFERRED_DEPTH 0x3
 #define DRM_CAP_DUMB_PREFER_SHADOW 0x4
 #define DRM_CAP_PRIME 0x5
+#define DRM_CAP_TIMESTAMP_MONOTONIC 0x6
 
 #define DRM_PRIME_CAP_IMPORT 0x1
 #define DRM_PRIME_CAP_EXPORT 0x2