diff --git a/watch.1 b/watch.1
index 1e823403..6ed933d2 100644
--- a/watch.1
+++ b/watch.1
@@ -15,8 +15,10 @@ program is run every 2 seconds.
 will run until interrupted.
 .SH OPTIONS
 .TP
-\fB\-d\fR, \fB\-\-differences\fR
-Highlight the differences between successive updates.
+\fB\-d\fR, \fB\-\-differences\fR [\fIpermanent\fR]
+Highlight the differences between successive updates.  Option will read
+optional argument that changes highlight to be permanent, allowing to see what
+has changed at least once since first iteration.
 .TP
 \fB\-n\fR, \fB\-\-interval\fR \fIseconds\fR
 Specify update interval.  The command will not allow quicker than 0.1 second
diff --git a/watch.c b/watch.c
index 2408e176..dc119868 100644
--- a/watch.c
+++ b/watch.c
@@ -67,7 +67,8 @@ static void __attribute__ ((__noreturn__))
 	fputs(USAGE_OPTIONS, out);
 	fputs(_("  -b, --beep             beep if command has a non-zero exit\n"
 		"  -c, --color            interpret ANSI color sequences\n"
-		"  -d, --differences      highlight changes between updates\n"
+		"  -d, --differences[=<permanent>]\n"
+                "                         highlight changes between updates\n"
 		"  -e, --errexit          exit if command has a non-zero exit\n"
 		"  -n, --interval <secs>  seconds to wait between updates\n"
 		"  -p, --precise          attempt run command in precise intervals\n"