diff --git a/man/man8/zinject.8 b/man/man8/zinject.8
index 50fecfb643..7f363974b3 100644
--- a/man/man8/zinject.8
+++ b/man/man8/zinject.8
@@ -111,6 +111,9 @@ Specify
 .BR "dtl" " for an ECHILD error,"
 .BR "io" " for an EIO error where reopening the device will succeed, or"
 .BR "nxio" " for an ENXIO error where reopening the device will fail."
+For EIO and ENXIO, the "failed" reads or writes still occur.  The probe simply
+sets the error value reported by the I/O pipeline so it appears the read or
+write failed.
 .TP
 .BI "\-f" " frequency"
 Only inject errors a fraction of the time. Expressed as a real number