diff --git a/cmd-set-option.c b/cmd-set-option.c
index 6c2d11ba..b04fd6ea 100644
--- a/cmd-set-option.c
+++ b/cmd-set-option.c
@@ -1,4 +1,4 @@
-/* $Id: cmd-set-option.c,v 1.71 2009-08-09 15:26:24 tcunha Exp $ */
+/* $Id: cmd-set-option.c,v 1.72 2009-08-09 16:48:34 tcunha Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicm@users.sourceforge.net>
@@ -31,8 +31,8 @@ int	cmd_set_option_exec(struct cmd *, struct cmd_ctx *);
 
 const struct cmd_entry cmd_set_option_entry = {
 	"set-option", "set",
-	CMD_OPTION_SESSION_USAGE,
-	0, CMD_CHFLAG('g')|CMD_CHFLAG('u'),
+	"[-agu] " CMD_OPTION_SESSION_USAGE,
+	0, CMD_CHFLAG('a')|CMD_CHFLAG('g')|CMD_CHFLAG('u'),
 	NULL,
 	cmd_option_parse,
 	cmd_set_option_exec,
@@ -144,7 +144,8 @@ cmd_set_option_exec(struct cmd *self, struct cmd_ctx *ctx)
 	} else {
 		switch (entry->type) {
 		case SET_OPTION_STRING:
-			set_option_string(ctx, oo, entry, data->value);
+			set_option_string(ctx, oo, entry,
+			    data->value, data->chflags & CMD_CHFLAG('a'));
 			break;
 		case SET_OPTION_NUMBER:
 			set_option_number(ctx, oo, entry, data->value);
diff --git a/cmd-set-window-option.c b/cmd-set-window-option.c
index ec10c79d..d93a4619 100644
--- a/cmd-set-window-option.c
+++ b/cmd-set-window-option.c
@@ -1,4 +1,4 @@
-/* $Id: cmd-set-window-option.c,v 1.36 2009-07-30 20:32:05 tcunha Exp $ */
+/* $Id: cmd-set-window-option.c,v 1.37 2009-08-09 16:48:34 tcunha Exp $ */
 
 /*
  * Copyright (c) 2008 Nicholas Marriott <nicm@users.sourceforge.net>
@@ -31,8 +31,8 @@ int	cmd_set_window_option_exec(struct cmd *, struct cmd_ctx *);
 
 const struct cmd_entry cmd_set_window_option_entry = {
 	"set-window-option", "setw",
-	CMD_OPTION_WINDOW_USAGE,
-	0, CMD_CHFLAG('g')|CMD_CHFLAG('u'),
+	"[-agu] " CMD_OPTION_WINDOW_USAGE,
+	0, CMD_CHFLAG('a')|CMD_CHFLAG('g')|CMD_CHFLAG('u'),
 	NULL,
 	cmd_option_parse,
 	cmd_set_window_option_exec,
@@ -134,7 +134,8 @@ cmd_set_window_option_exec(struct cmd *self, struct cmd_ctx *ctx)
 	} else {
 		switch (entry->type) {
 		case SET_OPTION_STRING:
-			set_option_string(ctx, oo, entry, data->value);
+			set_option_string(ctx, oo, entry,
+			    data->value, data->chflags & CMD_CHFLAG('a'));
 			break;
 		case SET_OPTION_NUMBER:
 			set_option_number(ctx, oo, entry, data->value);
diff --git a/options-cmd.c b/options-cmd.c
index 2c1ab636..e328fea2 100644
--- a/options-cmd.c
+++ b/options-cmd.c
@@ -1,4 +1,4 @@
-/* $Id: options-cmd.c,v 1.4 2009-01-27 20:22:33 nicm Exp $ */
+/* $Id: options-cmd.c,v 1.5 2009-08-09 16:48:34 tcunha Exp $ */
 
 /*
  * Copyright (c) 2008 Nicholas Marriott <nicm@users.sourceforge.net>
@@ -25,15 +25,26 @@
 
 void
 set_option_string(struct cmd_ctx *ctx, struct options *oo,
-    const struct set_option_entry *entry, char *value)
+    const struct set_option_entry *entry, char *value, int append)
 {
+	char	*oldvalue, *newvalue;
+
 	if (value == NULL) {
 		ctx->error(ctx, "empty value");
 		return;
 	}
 
-	options_set_string(oo, entry->name, "%s", value);
-	ctx->info(ctx, "set option: %s -> %s", entry->name, value);
+	if (append) {
+		oldvalue = options_get_string(oo, entry->name);
+		xasprintf(&newvalue, "%s%s", oldvalue, value);
+	} else
+		newvalue = value;
+		
+	options_set_string(oo, entry->name, "%s", newvalue);
+	ctx->info(ctx, "set option: %s -> %s", entry->name, newvalue);
+
+	if (newvalue != value)
+		xfree(newvalue);
 }
 
 void
diff --git a/tmux.h b/tmux.h
index 717c7f8a..448be4e6 100644
--- a/tmux.h
+++ b/tmux.h
@@ -1,4 +1,4 @@
-/* $Id: tmux.h,v 1.402 2009-08-09 15:26:24 tcunha Exp $ */
+/* $Id: tmux.h,v 1.403 2009-08-09 16:48:34 tcunha Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicm@users.sourceforge.net>
@@ -1171,7 +1171,7 @@ int	tty_keys_next(struct tty *, int *, u_char *);
 
 /* options-cmd.c */
 void	set_option_string(struct cmd_ctx *,
-	    struct options *, const struct set_option_entry *, char *);
+	    struct options *, const struct set_option_entry *, char *, int);
 void	set_option_number(struct cmd_ctx *,
     	    struct options *, const struct set_option_entry *, char *);
 void	set_option_key(struct cmd_ctx *,
@@ -1325,10 +1325,10 @@ void	cmd_buffer_init(struct cmd *, int);
 int	cmd_buffer_parse(struct cmd *, int, char **, char **);
 void	cmd_buffer_free(struct cmd *);
 size_t	cmd_buffer_print(struct cmd *, char *, size_t);
-#define CMD_OPTION_PANE_USAGE "[-gu] [-t target-pane] option [value]"
-#define CMD_OPTION_WINDOW_USAGE "[-gu] [-t target-window] option [value]"
-#define CMD_OPTION_SESSION_USAGE "[-gu] [-t target-session] option [value]"
-#define CMD_OPTION_CLIENT_USAGE "[-gu] [-t target-client] option [value]"
+#define CMD_OPTION_PANE_USAGE "[-t target-pane] option [value]"
+#define CMD_OPTION_WINDOW_USAGE "[-t target-window] option [value]"
+#define CMD_OPTION_SESSION_USAGE "[-t target-session] option [value]"
+#define CMD_OPTION_CLIENT_USAGE "[-t target-client] option [value]"
 void	cmd_option_init(struct cmd *, int);
 int	cmd_option_parse(struct cmd *, int, char **, char **);
 void	cmd_option_free(struct cmd *);