diff --git a/dmenu.1 b/dmenu.1
index 323f93c..1ae3fe3 100644
--- a/dmenu.1
+++ b/dmenu.1
@@ -22,6 +22,8 @@ dmenu \- dynamic menu
 .IR color ]
 .RB [ \-w
 .IR windowid ]
+.RB [ \-dy
+.IR command ]
 .P
 .BR dmenu_run " ..."
 .SH DESCRIPTION
@@ -80,6 +82,9 @@ prints version information to stdout, then exits.
 .TP
 .BI \-w " windowid"
 embed into windowid.
+.TP
+.BI \-dy " command"
+runs command whenever input changes to update menu items.
 .SH USAGE
 dmenu is completely controlled by the keyboard.  Items are selected using the
 arrow keys, page up, page down, home, and end.
diff --git a/dmenu.c b/dmenu.c
index 65f25ce..6780122 100644
--- a/dmenu.c
+++ b/dmenu.c
@@ -519,14 +571,14 @@ paste(void)
 }
 
 static void
-readstdin(void)
+readstdin(FILE* stream)
 {
 	char buf[sizeof text], *p;
 	size_t i, imax = 0, size = 0;
 	unsigned int tmpmax = 0;
 
 	/* read each line from stdin and add it to the item list */
-	for (i = 0; fgets(buf, sizeof buf, stdin); i++) {
+	for (i = 0; fgets(buf, sizeof buf, stream); i++) {
 		if (i + 1 >= size / sizeof *items)
 			if (!(items = realloc(items, (size += BUFSIZ))))
 				die("cannot realloc %u bytes:", size);
@@ -544,7 +596,7 @@ readstdin(void)
 	if (items)
 		items[i].text = NULL;
 	inputw = items ? TEXTW(items[imax].text) : 0;
-	lines = MIN(lines, i);
+	lines = MIN(max_lines, i);
 }
 
 static void
@@ -690,7 +742,8 @@ static void
 usage(void)
 {
 	fputs("usage: dmenu [-bfiv] [-l lines] [-p prompt] [-fn font] [-m monitor]\n"
-	      "             [-nb color] [-nf color] [-sb color] [-sf color] [-w windowid]\n", stderr);
+	      "             [-nb color] [-nf color] [-sb color] [-sf color] [-w windowid]\n"
+	      "             [-dy command]\n", stderr);
 	exit(1);
 }
 
@@ -733,6 +786,8 @@ main(int argc, char *argv[])
 			colors[SchemeSel][ColFg] = argv[++i];
 		else if (!strcmp(argv[i], "-w"))   /* embedding window id */
 			embed = argv[++i];
+		else if (!strcmp(argv[i], "-dy"))  /* dynamic command to run */
+			dynamic = argv[++i] && *argv[i] ? argv[i] : NULL;
 		else
 			usage();
 
@@ -757,11 +812,14 @@ main(int argc, char *argv[])
 		die("pledge");
 #endif
 
+	max_lines = lines;
 	if (fast && !isatty(0)) {
 		grabkeyboard();
-		readstdin();
+		if (!dynamic)
+			readstdin(stdin);
 	} else {
-		readstdin();
+		if (!dynamic)
+			readstdin(stdin);
 		grabkeyboard();
 	}
 	setup();
-- 
2.34.1