diff --git a/compiler-rt/lib/tsan/rtl-old/tsan_shadow.h b/compiler-rt/lib/tsan/rtl-old/tsan_shadow.h
index 8b7bc341713e87..566584fd3203a8 100644
--- a/compiler-rt/lib/tsan/rtl-old/tsan_shadow.h
+++ b/compiler-rt/lib/tsan/rtl-old/tsan_shadow.h
@@ -94,6 +94,7 @@ class FastState {
 // Shadow (from most significant bit):
 //   freed           : 1
 //   tid             : kTidBits
+//   unused          : 1
 //   is_atomic       : 1
 //   is_read         : 1
 //   size_log        : 2