diff --git a/config.h b/config.h
index c1f1cba..6ac6cdf 100644
--- a/config.h
+++ b/config.h
@@ -45,7 +45,8 @@ static const Rule rules[] = {
 	 */
 	/* class      instance    title       tags mask     isfloating   monitor */
 	{ "Gimp",     NULL,       NULL,       0,            1,           -1 },
-	{ "Firefox",  NULL,       NULL,       2,            0,           -1 },
+	{ "firefox",  NULL,       NULL,       2,            0,           -1 },
+	{ "URxvt",    "cal",       NULL,       0,            1,           -1 },
 };
 
 /* layout(s) */