diff --git a/Makefile b/Makefile
index 775b2ed..1344536 100644
--- a/Makefile
+++ b/Makefile
@@ -58,10 +58,10 @@ TARGET = graftcp $(GRAFTCP_LOCAL_BIN)
 all:: $(TARGET)
 
 
-graftcp: main.o graftcp.o util.o string-set.o cidr-trie.o conf.o
+graftcp: main.o graftcp.o util.o cidr-trie.o conf.o
 	$(CC) $^ -o $@
 
-libgraftcp.a: graftcp.o util.o string-set.o cidr-trie.o conf.o
+libgraftcp.a: graftcp.o util.o cidr-trie.o conf.o
 	$(AR) rcs $@ $^
 
 %.o: %.c
diff --git a/string-set.c b/string-set.c
deleted file mode 100644
index 8625758..0000000
--- a/string-set.c
+++ /dev/null
@@ -1,136 +0,0 @@
-/*
- * graftcp
- * Copyright (C) 2018 Hmgle <dustgle@gmail.com>
- *
- * This program is free software: you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- */
-#include <stdio.h>
-#include <string.h>
-#include <stdlib.h>
-#include <assert.h>
-#include <errno.h>
-
-#include "string-set.h"
-
-/* see http://www.cse.yorku.ca/~oz/hash.html */
-static unsigned long str_hash(const char *str)
-{
-	unsigned long hash = 5381;
-	int c;
-
-	while ((c = *str++) != '\0')
-		hash = ((hash << 5) + hash) + c;	/* hash * 33 + c */
-
-	return hash;
-}
-
-struct str_set *str_set_new()
-{
-	struct str_set *set;
-	int i;
-
-	set = calloc(1, sizeof(*set) + 509 * sizeof(set->buckets[0]));
-	if (!set) {
-		fprintf(stderr, "calloc: %s\n", strerror(errno));
-		exit(1);
-	}
-	set->size = 509;
-	set->buckets = (struct member **)(set + 1);
-	for (i = 0; i < set->size; i++)
-		set->buckets[i] = NULL;
-	set->length = 0;
-	return set;
-}
-
-void str_set_put(struct str_set *set, const char *elem)
-{
-	int i;
-	struct member *p;
-
-	assert(set);
-	assert(elem);
-	i = str_hash(elem) % set->size;
-	for (p = set->buckets[i]; p; p = p->link) {
-		if (strcmp(elem, p->element) == 0)
-			break;
-	}
-	if (p == NULL) {
-		p = calloc(1, sizeof(*p));
-		if (!p) {
-			fprintf(stderr, "calloc: %s\n", strerror(errno));
-			exit(1);
-		}
-		p->element = elem;
-		p->link = set->buckets[i];
-		set->buckets[i] = p;
-		set->length++;
-	} else {
-		p->element = elem;
-	}
-}
-
-char *str_set_remove(struct str_set *set, const char *elem)
-{
-	int i;
-	struct member **pp;
-
-	assert(set);
-	assert(elem);
-	i = str_hash(elem) % set->size;
-	for (pp = &set->buckets[i]; *pp; pp = &(*pp)->link) {
-		if (strcmp(elem, (*pp)->element) == 0) {
-			struct member *p = *pp;
-			*pp = p->link;
-			elem = p->element;
-			free(p);
-			set->length--;
-			return (char *)elem;
-		}
-	}
-	return NULL;
-}
-
-int str_set_length(struct str_set *set)
-{
-	assert(set);
-	return set->length;
-}
-
-int is_str_set_member(struct str_set *set, const void *elem)
-{
-	int i;
-	struct member *p;
-
-	assert(set);
-	assert(elem);
-	i = str_hash(elem) % set->size;
-	for (p = set->buckets[i]; p; p = p->link) {
-		if (strcmp(elem, p->element) == 0)
-			break;
-	}
-	return p != NULL;
-}
-
-void str_set_free(struct str_set **set)
-{
-	assert(set && *set);
-	if ((*set)->length > 0) {
-		int i;
-		struct member *p, *q;
-		for (i = 0; i < (*set)->size; i++) {
-			for (p = (*set)->buckets[i]; p; p = q) {
-				q = p->link;
-				free(p);
-			}
-		}
-	}
-	free(*set);
-}
diff --git a/string-set.h b/string-set.h
deleted file mode 100644
index fcb8845..0000000
--- a/string-set.h
+++ /dev/null
@@ -1,34 +0,0 @@
-/*
- * graftcp
- * Copyright (C) 2018 Hmgle <dustgle@gmail.com>
- *
- * This program is free software: you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- */
-#ifndef STRING_SET_H
-#define STRING_SET_H
-
-struct str_set {
-	int length;
-	int size;
-	struct member {
-		struct member *link;
-		const char *element;
-	} **buckets;
-};
-
-struct str_set *str_set_new();
-void str_set_put(struct str_set *set, const char *elem);
-char *str_set_remove(struct str_set *set, const char *elem);
-int str_set_length(struct str_set *set);
-int is_str_set_member(struct str_set *set, const void *elem);
-void str_set_free(struct str_set **set);
-
-#endif