diff --git a/src/shrpx-unittest.cc b/src/shrpx-unittest.cc
index d38acb5a..1e9cda83 100644
--- a/src/shrpx-unittest.cc
+++ b/src/shrpx-unittest.cc
@@ -126,6 +126,8 @@ int main(int argc, char *argv[]) {
       !CU_add_test(pSuite, "util_utox", shrpx::test_util_utox) ||
       !CU_add_test(pSuite, "util_http_date", shrpx::test_util_http_date) ||
       !CU_add_test(pSuite, "util_select_h2", shrpx::test_util_select_h2) ||
+      !CU_add_test(pSuite, "util_ipv6_numeric_addr",
+                   shrpx::test_util_ipv6_numeric_addr) ||
       !CU_add_test(pSuite, "gzip_inflate", test_nghttp2_gzip_inflate) ||
       !CU_add_test(pSuite, "ringbuf_write", nghttp2::test_ringbuf_write) ||
       !CU_add_test(pSuite, "ringbuf_iovec", nghttp2::test_ringbuf_iovec)) {
diff --git a/src/shrpx.cc b/src/shrpx.cc
index 15140d69..9f14c91e 100644
--- a/src/shrpx.cc
+++ b/src/shrpx.cc
@@ -84,13 +84,6 @@ const int GRACEFUL_SHUTDOWN_SIGNAL = SIGQUIT;
 // binary is listening to.
 #define ENV_PORT "NGHTTPX_PORT"
 
-namespace {
-bool is_ipv6_numeric_addr(const char *host) {
-  uint8_t dst[16];
-  return inet_pton(AF_INET6, host, dst) == 1;
-}
-} // namespace
-
 namespace {
 int resolve_hostname(sockaddr_union *addr, size_t *addrlen,
                      const char *hostname, uint16_t port, int family) {
@@ -1805,7 +1798,7 @@ int main(int argc, char **argv) {
   }
 
   for (auto &addr : mod_config()->downstream_addrs) {
-    auto ipv6 = is_ipv6_numeric_addr(addr.host.get());
+    auto ipv6 = util::ipv6_numeric_addr(addr.host.get());
     std::string hostport;
 
     if (ipv6) {
diff --git a/src/util.cc b/src/util.cc
index a4ab3f46..4016d955 100644
--- a/src/util.cc
+++ b/src/util.cc
@@ -32,6 +32,7 @@
 #include <fcntl.h>
 #include <netinet/in.h>
 #include <netinet/tcp.h>
+#include <arpa/inet.h>
 
 #include <cassert>
 #include <cstdio>
@@ -881,6 +882,11 @@ bool check_socket_connected(int fd) {
   return true;
 }
 
+bool ipv6_numeric_addr(const char *host) {
+  uint8_t dst[16];
+  return inet_pton(AF_INET6, host, dst) == 1;
+}
+
 } // namespace util
 
 } // namespace nghttp2
diff --git a/src/util.h b/src/util.h
index a8150abf..8efd4e4b 100644
--- a/src/util.h
+++ b/src/util.h
@@ -474,6 +474,9 @@ int create_nonblock_socket(int family);
 
 bool check_socket_connected(int fd);
 
+// Returns true if |host| is IPv6 numeric address (e.g., ::1)
+bool ipv6_numeric_addr(const char *host);
+
 } // namespace util
 
 } // namespace nghttp2
diff --git a/src/util_test.cc b/src/util_test.cc
index cbfb692c..12d3bbb6 100644
--- a/src/util_test.cc
+++ b/src/util_test.cc
@@ -165,4 +165,13 @@ void test_util_select_h2(void) {
   CU_ASSERT(NGHTTP2_H2_PROTO_ALIAS_LEN == outlen);
 }
 
+void test_util_ipv6_numeric_addr(void) {
+  CU_ASSERT(util::ipv6_numeric_addr("::1"));
+  CU_ASSERT(util::ipv6_numeric_addr("2001:0db8:85a3:0042:1000:8a2e:0370:7334"));
+  // IPv4
+  CU_ASSERT(!util::ipv6_numeric_addr("127.0.0.1"));
+  // not numeric address
+  CU_ASSERT(!util::ipv6_numeric_addr("localhost"));
+}
+
 } // namespace shrpx
diff --git a/src/util_test.h b/src/util_test.h
index 9d258d00..1fe123a7 100644
--- a/src/util_test.h
+++ b/src/util_test.h
@@ -36,6 +36,7 @@ void test_util_quote_string(void);
 void test_util_utox(void);
 void test_util_http_date(void);
 void test_util_select_h2(void);
+void test_util_ipv6_numeric_addr(void);
 
 } // namespace shrpx