diff --git a/src/h2load_http1_session.cc b/src/h2load_http1_session.cc
index b1fddccb..6080e1fb 100644
--- a/src/h2load_http1_session.cc
+++ b/src/h2load_http1_session.cc
@@ -146,7 +146,7 @@ int htp_body_cb(http_parser *htp, const char *data, size_t len) {
 } // namespace
 
 namespace {
-http_parser_settings htp_hooks = {
+constexpr http_parser_settings htp_hooks = {
     htp_msg_begincb,   // http_cb      on_message_begin;
     nullptr,           // http_data_cb on_url;
     htp_statuscb,      // http_data_cb on_status;
diff --git a/src/nghttp.cc b/src/nghttp.cc
index 12f7d362..badbc9ca 100644
--- a/src/nghttp.cc
+++ b/src/nghttp.cc
@@ -371,7 +371,7 @@ int htp_msg_completecb(http_parser *htp) {
 } // namespace
 
 namespace {
-http_parser_settings htp_hooks = {
+constexpr http_parser_settings htp_hooks = {
     htp_msg_begincb,   // http_cb      on_message_begin;
     nullptr,           // http_data_cb on_url;
     htp_statuscb,      // http_data_cb on_status;
diff --git a/src/shrpx.cc b/src/shrpx.cc
index a77efd0b..eaa9afc6 100644
--- a/src/shrpx.cc
+++ b/src/shrpx.cc
@@ -2911,7 +2911,7 @@ int main(int argc, char **argv) {
 
   while (1) {
     static int flag = 0;
-    static option long_options[] = {
+    static constexpr option long_options[] = {
         {SHRPX_OPT_DAEMON.c_str(), no_argument, nullptr, 'D'},
         {SHRPX_OPT_LOG_LEVEL.c_str(), required_argument, nullptr, 'L'},
         {SHRPX_OPT_BACKEND.c_str(), required_argument, nullptr, 'b'},
diff --git a/src/shrpx_http2_session.cc b/src/shrpx_http2_session.cc
index 1c7c6f37..65f16aaa 100644
--- a/src/shrpx_http2_session.cc
+++ b/src/shrpx_http2_session.cc
@@ -638,7 +638,7 @@ int htp_hdrs_completecb(http_parser *htp) {
 } // namespace
 
 namespace {
-http_parser_settings htp_hooks = {
+constexpr http_parser_settings htp_hooks = {
     nullptr,             // http_cb      on_message_begin;
     nullptr,             // http_data_cb on_url;
     nullptr,             // http_data_cb on_status;
diff --git a/src/shrpx_http_downstream_connection.cc b/src/shrpx_http_downstream_connection.cc
index 3a073bd1..85a72b76 100644
--- a/src/shrpx_http_downstream_connection.cc
+++ b/src/shrpx_http_downstream_connection.cc
@@ -1070,7 +1070,7 @@ int htp_msg_completecb(http_parser *htp) {
 } // namespace
 
 namespace {
-http_parser_settings htp_hooks = {
+constexpr http_parser_settings htp_hooks = {
     htp_msg_begincb,     // http_cb on_message_begin;
     nullptr,             // http_data_cb on_url;
     nullptr,             // http_data_cb on_status;
diff --git a/src/shrpx_https_upstream.cc b/src/shrpx_https_upstream.cc
index b9a5df00..0c2b28b3 100644
--- a/src/shrpx_https_upstream.cc
+++ b/src/shrpx_https_upstream.cc
@@ -505,7 +505,7 @@ int htp_msg_completecb(http_parser *htp) {
 } // namespace
 
 namespace {
-http_parser_settings htp_hooks = {
+constexpr http_parser_settings htp_hooks = {
     htp_msg_begin,       // http_cb      on_message_begin;
     htp_uricb,           // http_data_cb on_url;
     nullptr,             // http_data_cb on_status;
diff --git a/src/util.cc b/src/util.cc
index cd0f5cc8..410c2704 100644
--- a/src/util.cc
+++ b/src/util.cc
@@ -472,7 +472,7 @@ int levenshtein(const char *a, int alen, const char *b, int blen, int swapcost,
 }
 } // namespace
 
-void show_candidates(const char *unkopt, option *options) {
+void show_candidates(const char *unkopt, const option *options) {
   for (; *unkopt == '-'; ++unkopt)
     ;
   if (*unkopt == '\0') {
diff --git a/src/util.h b/src/util.h
index d2f4d9f1..cda97a05 100644
--- a/src/util.h
+++ b/src/util.h
@@ -184,7 +184,7 @@ time_t parse_http_date(const StringRef &s);
 char upcase(char c);
 
 inline char lowcase(char c) {
-  static unsigned char tbl[] = {
+  constexpr static unsigned char tbl[] = {
       0,   1,   2,   3,   4,   5,   6,   7,   8,   9,   10,  11,  12,  13,  14,
       15,  16,  17,  18,  19,  20,  21,  22,  23,  24,  25,  26,  27,  28,  29,
       30,  31,  32,  33,  34,  35,  36,  37,  38,  39,  40,  41,  42,  43,  44,
@@ -451,7 +451,7 @@ void to_token68(std::string &base64str);
 
 StringRef to_base64(BlockAllocator &balloc, const StringRef &token68str);
 
-void show_candidates(const char *unkopt, option *options);
+void show_candidates(const char *unkopt, const option *options);
 
 bool has_uri_field(const http_parser_url &u, http_parser_url_fields field);