diff --git a/cmd-set-option.c b/cmd-set-option.c
index d1b7f331..ab15eb70 100644
--- a/cmd-set-option.c
+++ b/cmd-set-option.c
@@ -292,10 +292,8 @@ cmd_set_option_user(struct cmd *self, struct cmdq_item *item,
 			cmdq_error(item, "empty value");
 			return (CMD_RETURN_ERROR);
 		}
-		if (o != NULL && args_has(args, 'a'))
-			options_set_string(oo, optstr, "%s%s", o->str, valstr);
-		else
-			options_set_string(oo, optstr, "%s", valstr);
+		options_set_string(oo, optstr, args_has(args, 'a'), "%s",
+		    valstr);
 	}
 	return (CMD_RETURN_NORMAL);
 }
@@ -316,10 +314,11 @@ cmd_set_option_unset(struct cmd *self, struct cmdq_item *item,
 	if (args_has(args, 'g') || oo == global_options) {
 		switch (oe->type) {
 		case OPTIONS_TABLE_STRING:
-			options_set_string(oo, oe->name, "%s", oe->default_str);
+			options_set_string(oo, oe->name, 0, "%s",
+			    oe->default_str);
 			break;
 		case OPTIONS_TABLE_STYLE:
-			options_set_style(oo, oe->name, oe->default_str, 0);
+			options_set_style(oo, oe->name, 0, oe->default_str);
 			break;
 		default:
 			options_set_number(oo, oe->name, oe->default_num);
@@ -391,20 +390,10 @@ cmd_set_option_string(struct cmd *self, __unused struct cmdq_item *item,
     const struct options_table_entry *oe, struct options *oo,
     const char *value)
 {
-	struct args		*args = self->args;
-	struct options_entry	*o;
-	char			*oldval, *newval;
+	struct args	*args = self->args;
+	int		 append = args_has(args, 'a');
 
-	if (args_has(args, 'a')) {
-		oldval = options_get_string(oo, oe->name);
-		xasprintf(&newval, "%s%s", oldval, value);
-	} else
-		newval = xstrdup(value);
-
-	o = options_set_string(oo, oe->name, "%s", newval);
-
-	free(newval);
-	return (o);
+	return (options_set_string(oo, oe->name, append, "%s", value));
 }
 
 /* Set a number option. */
@@ -544,11 +533,10 @@ cmd_set_option_style(struct cmd *self, struct cmdq_item *item,
     const char *value)
 {
 	struct args		*args = self->args;
+	int			 append = args_has(args, 'a');
 	struct options_entry	*o;
-	int			 append;
 
-	append = args_has(args, 'a');
-	if ((o = options_set_style(oo, oe->name, value, append)) == NULL) {
+	if ((o = options_set_style(oo, oe->name, append, value)) == NULL) {
 		cmdq_error(item, "bad style: %s", value);
 		return (NULL);
 	}
diff --git a/options-table.c b/options-table.c
index a6bdda6f..92441ebe 100644
--- a/options-table.c
+++ b/options-table.c
@@ -915,10 +915,11 @@ options_table_populate_tree(enum options_table_scope scope, struct options *oo)
 			continue;
 		switch (oe->type) {
 		case OPTIONS_TABLE_STRING:
-			options_set_string(oo, oe->name, "%s", oe->default_str);
+			options_set_string(oo, oe->name, 0, "%s",
+			    oe->default_str);
 			break;
 		case OPTIONS_TABLE_STYLE:
-			options_set_style(oo, oe->name, oe->default_str, 0);
+			options_set_style(oo, oe->name, 0, oe->default_str);
 			break;
 		default:
 			options_set_number(oo, oe->name, oe->default_num);
diff --git a/options.c b/options.c
index cb7f3d87..09e8669a 100644
--- a/options.c
+++ b/options.c
@@ -65,24 +65,17 @@ options_free1(struct options *oo, struct options_entry *o)
 }
 
 static struct options_entry *
-options_new(struct options *oo, const char *name, char **s)
+options_new(struct options *oo, const char *name)
 {
 	struct options_entry	*o;
 
-	if (s != NULL)
-		*s = NULL;
-
 	if ((o = options_find1(oo, name)) == NULL) {
 		o = xmalloc(sizeof *o);
 		o->name = xstrdup(name);
 		RB_INSERT(options_tree, &oo->tree, o);
 		memcpy(&o->style, &grid_default_cell, sizeof o->style);
-	} else if (o->type == OPTIONS_STRING) {
-		if (s != NULL)
-			*s = o->str;
-		else
-			free(o->str);
-	}
+	} else if (o->type == OPTIONS_STRING)
+		free(o->str);
 	return (o);
 }
 
@@ -143,20 +136,29 @@ options_remove(struct options *oo, const char *name)
 }
 
 struct options_entry *
-options_set_string(struct options *oo, const char *name, const char *fmt, ...)
+options_set_string(struct options *oo, const char *name, int append,
+    const char *fmt, ...)
 {
 	struct options_entry	*o;
 	va_list			 ap;
-	char			*s;
+	char			*s, *value;
 
 	va_start(ap, fmt);
-
-	o = options_new(oo, name, &s);
-	o->type = OPTIONS_STRING;
-	xvasprintf(&o->str, fmt, ap);
-	free(s);
-
+	xvasprintf(&s, fmt, ap);
 	va_end(ap);
+
+	o = options_find1(oo, name);
+	if (o == NULL || !append)
+		value = s;
+	else {
+		xasprintf(&value, "%s%s", s, o->str);
+		free(s);
+	}
+
+	o = options_new(oo, name);
+	o->type = OPTIONS_STRING;
+	o->str = value;
+
 	return (o);
 }
 
@@ -177,7 +179,7 @@ options_set_number(struct options *oo, const char *name, long long value)
 {
 	struct options_entry	*o;
 
-	o = options_new(oo, name, NULL);
+	o = options_new(oo, name);
 	o->type = OPTIONS_NUMBER;
 	o->num = value;
 
@@ -197,8 +199,8 @@ options_get_number(struct options *oo, const char *name)
 }
 
 struct options_entry *
-options_set_style(struct options *oo, const char *name, const char *value,
-    int append)
+options_set_style(struct options *oo, const char *name, int append,
+    const char *value)
 {
 	struct options_entry	*o;
 	struct grid_cell	 tmpgc;
@@ -212,7 +214,7 @@ options_set_style(struct options *oo, const char *name, const char *value,
 	if (style_parse(&grid_default_cell, &tmpgc, value) == -1)
 		return (NULL);
 
-	o = options_new(oo, name, NULL);
+	o = options_new(oo, name);
 	o->type = OPTIONS_STYLE;
 	memcpy(&o->style, &tmpgc, sizeof o->style);
 
diff --git a/style.c b/style.c
index 8af739e5..f4a8f05f 100644
--- a/style.c
+++ b/style.c
@@ -143,7 +143,7 @@ style_update_new(struct options *oo, const char *name, const char *newname)
 
 	o = options_find1(oo, newname);
 	if (o == NULL)
-		o = options_set_style(oo, newname, "default", 0);
+		o = options_set_style(oo, newname, 0, "default");
 	gc = &o->style;
 
 	o = options_find1(oo, name);
diff --git a/tmux.c b/tmux.c
index 194a16e5..664ff0c5 100644
--- a/tmux.c
+++ b/tmux.c
@@ -295,7 +295,8 @@ main(int argc, char **argv)
 
 	global_s_options = options_create(NULL);
 	options_table_populate_tree(OPTIONS_TABLE_SESSION, global_s_options);
-	options_set_string(global_s_options, "default-shell", "%s", getshell());
+	options_set_string(global_s_options, "default-shell", 0, "%s",
+	    getshell());
 
 	global_w_options = options_create(NULL);
 	options_table_populate_tree(OPTIONS_TABLE_WINDOW, global_w_options);
diff --git a/tmux.h b/tmux.h
index 24c8dd11..fa157a1c 100644
--- a/tmux.h
+++ b/tmux.h
@@ -1627,14 +1627,14 @@ struct options_entry *options_next(struct options_entry *);
 struct options_entry *options_find1(struct options *, const char *);
 struct options_entry *options_find(struct options *, const char *);
 void	options_remove(struct options *, const char *);
-struct options_entry *printflike(3, 4) options_set_string(struct options *,
-	    const char *, const char *, ...);
+struct options_entry * printflike(4, 5) options_set_string(struct options *,
+	    const char *, int, const char *, ...);
 char   *options_get_string(struct options *, const char *);
 struct options_entry *options_set_number(struct options *, const char *,
 	    long long);
 long long options_get_number(struct options *, const char *);
-struct options_entry *options_set_style(struct options *, const char *,
-	    const char *, int);
+struct options_entry *options_set_style(struct options *, const char *, int,
+	    const char *);
 struct grid_cell *options_get_style(struct options *, const char *);
 
 /* options-table.c */