diff --git a/headers/os/kernel/OS.h b/headers/os/kernel/OS.h
index e40449e377..741a9d318c 100644
--- a/headers/os/kernel/OS.h
+++ b/headers/os/kernel/OS.h
@@ -37,6 +37,9 @@ enum {
 	B_TIMEOUT_REAL_TIME_BASE		= 0x40,
 	B_ABSOLUTE_REAL_TIME_TIMEOUT	= B_ABSOLUTE_TIMEOUT
 										| B_TIMEOUT_REAL_TIME_BASE
+								/* fails after an absolute timeout
+												with B_TIMED_OUT based on the
+												real time clock */
 };