diff --git a/man2/clock_getres.2 b/man2/clock_getres.2
index 99913370b..99e4f64d9 100644
--- a/man2/clock_getres.2
+++ b/man2/clock_getres.2
@@ -133,6 +133,9 @@ and NTP.
 A faster but less precise version of
 .BR CLOCK_REALTIME .
 Use when you need very fast, but not fine-grained timestamps.
+Requires per-architecture support,
+and probably also architecture support for this flag in the
+.BR vdso (7).
 .TP
 .B CLOCK_MONOTONIC
 Clock that cannot be set and represents monotonic time since
@@ -148,6 +151,9 @@ and NTP.
 A faster but less precise version of
 .BR CLOCK_MONOTONIC .
 Use when you need very fast, but not fine-grained timestamps.
+Requires per-architecture support,
+and probably also architecture support for this flag in the
+.BR vdso (7).
 .TP
 .BR CLOCK_MONOTONIC_RAW " (since Linux 2.6.28; Linux-specific)"
 .\" Added in commit 2d42244ae71d6c7b0884b5664cf2eda30fb2ae68, John Stultz