diff --git a/src/http2.h b/src/http2.h
index 7fa42b37..aaf076d6 100644
--- a/src/http2.h
+++ b/src/http2.h
@@ -340,7 +340,8 @@ std::string normalize_path(InputIt first, InputIt last) {
   } else {
     for (; first < last - 2;) {
       if (*first == '%') {
-        if (util::isHexDigit(*(first + 1)) && util::isHexDigit(*(first + 2))) {
+        if (util::is_hex_digit(*(first + 1)) &&
+            util::is_hex_digit(*(first + 2))) {
           auto c = (util::hex_to_uint(*(first + 1)) << 4) +
                    util::hex_to_uint(*(first + 2));
           if (util::in_rfc3986_unreserved_chars(c)) {
diff --git a/src/shrpx_client_handler.cc b/src/shrpx_client_handler.cc
index 47818894..8ace9d4a 100644
--- a/src/shrpx_client_handler.cc
+++ b/src/shrpx_client_handler.cc
@@ -859,13 +859,13 @@ ssize_t parse_proxy_line_port(const uint8_t *first, const uint8_t *last) {
   }
 
   if (*p == '0') {
-    if (p + 1 != last && util::isDigit(*(p + 1))) {
+    if (p + 1 != last && util::is_digit(*(p + 1))) {
       return -1;
     }
     return 1;
   }
 
-  for (; p != last && util::isDigit(*p); ++p) {
+  for (; p != last && util::is_digit(*p); ++p) {
     port *= 10;
     port += *p - '0';
 
diff --git a/src/shrpx_config.cc b/src/shrpx_config.cc
index c9b229eb..565d3118 100644
--- a/src/shrpx_config.cc
+++ b/src/shrpx_config.cc
@@ -471,7 +471,7 @@ LogFragmentType log_var_lookup_token(const char *name, size_t namelen) {
 
 namespace {
 bool var_token(char c) {
-  return util::isAlpha(c) || util::isDigit(c) || c == '_';
+  return util::is_alpha(c) || util::is_digit(c) || c == '_';
 }
 } // namespace
 
diff --git a/src/util.cc b/src/util.cc
index 2962e152..90ace89a 100644
--- a/src/util.cc
+++ b/src/util.cc
@@ -67,7 +67,7 @@ const char UPPER_XDIGITS[] = "0123456789ABCDEF";
 
 bool in_rfc3986_unreserved_chars(const char c) {
   static constexpr const char unreserved[] = {'-', '.', '_', '~'};
-  return isAlpha(c) || isDigit(c) ||
+  return is_alpha(c) || is_digit(c) ||
          std::find(std::begin(unreserved), std::end(unreserved), c) !=
              std::end(unreserved);
 }
@@ -120,7 +120,7 @@ bool in_token(char c) {
   static constexpr const char extra[] = {'!',  '#', '$', '%', '&',
                                          '\'', '*', '+', '-', '.',
                                          '^',  '_', '`', '|', '~'};
-  return isAlpha(c) || isDigit(c) ||
+  return is_alpha(c) || is_digit(c) ||
          std::find(std::begin(extra), std::end(extra), c) != std::end(extra);
 }
 
diff --git a/src/util.h b/src/util.h
index a4468bcb..9319e7cd 100644
--- a/src/util.h
+++ b/src/util.h
@@ -64,14 +64,14 @@ constexpr const char NGHTTP2_H1_1[] = "http/1.1";
 
 namespace util {
 
-inline bool isAlpha(const char c) {
+inline bool is_alpha(const char c) {
   return ('A' <= c && c <= 'Z') || ('a' <= c && c <= 'z');
 }
 
-inline bool isDigit(const char c) { return '0' <= c && c <= '9'; }
+inline bool is_digit(const char c) { return '0' <= c && c <= '9'; }
 
-inline bool isHexDigit(const char c) {
-  return isDigit(c) || ('A' <= c && c <= 'F') || ('a' <= c && c <= 'f');
+inline bool is_hex_digit(const char c) {
+  return is_digit(c) || ('A' <= c && c <= 'F') || ('a' <= c && c <= 'f');
 }
 
 bool in_rfc3986_unreserved_chars(const char c);
@@ -84,7 +84,7 @@ bool in_token(char c);
 bool in_attr_char(char c);
 
 // Returns integer corresponding to hex notation |c|.  It is undefined
-// if isHexDigit(c) is false.
+// if is_hex_digit(c) is false.
 uint32_t hex_to_uint(char c);
 
 std::string percent_encode(const unsigned char *target, size_t len);
@@ -99,8 +99,8 @@ std::string percent_decode(InputIt first, InputIt last) {
   std::string result;
   for (; first != last; ++first) {
     if (*first == '%') {
-      if (first + 1 != last && first + 2 != last && isHexDigit(*(first + 1)) &&
-          isHexDigit(*(first + 2))) {
+      if (first + 1 != last && first + 2 != last &&
+          is_hex_digit(*(first + 1)) && is_hex_digit(*(first + 2))) {
         result += (hex_to_uint(*(first + 1)) << 4) + hex_to_uint(*(first + 2));
         first += 2;
         continue;