diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index eeb787b1c53c72771c8d684154b7a87dc029a45b..f35eb72739c09e3ad0bd22e279fa4a33119c15f6 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -144,7 +144,7 @@ enum perf_event_sample_format {
 
 	PERF_SAMPLE_MAX = 1U << 20,		/* non-ABI */
 
-	__PERF_SAMPLE_CALLCHAIN_EARLY		= 1ULL << 63,
+	__PERF_SAMPLE_CALLCHAIN_EARLY		= 1ULL << 63, /* non-ABI; internal use */
 };
 
 /*