diff --git a/man2/perf_event_open.2 b/man2/perf_event_open.2
index ce733bb03..a8821eff7 100644
--- a/man2/perf_event_open.2
+++ b/man2/perf_event_open.2
@@ -961,7 +961,9 @@ Extra support is needed for handling hypervisor measurements on most
 machines.
 .TP
 .IR "exclude_idle"
-If set, don't count when the CPU is idle.
+If set, don't count when the CPU is running the idle task.
+While you can currently enable this for any event type, it is ignored
+for all but software events.
 .TP
 .IR "mmap"
 The