diff --git a/include/ada/idna/identifier.h b/include/ada/idna/identifier.h
index 20428a7..1e5ab04 100644
--- a/include/ada/idna/identifier.h
+++ b/include/ada/idna/identifier.h
@@ -6,7 +6,6 @@
 
 namespace ada::idna {
 
-// Access the first code point of the input string.
 // Verify if it is valid name code point given a Unicode code point and a
 // boolean first: If first is true return the result of checking if code point
 // is contained in the IdentifierStart set of code points. Otherwise return the
@@ -14,7 +13,7 @@ namespace ada::idna {
 // code points. Returns false if the input is empty or the code point is not
 // valid. There is minimal Unicode error handling: the input should be valid
 // UTF-8. https://urlpattern.spec.whatwg.org/#is-a-valid-name-code-point
-bool valid_name_code_point(std::string_view input, bool first);
+bool valid_name_code_point(char32_t code_point, bool first);
 
 }  // namespace ada::idna
 
diff --git a/src/identifier.cpp b/src/identifier.cpp
index f9e9b74..1e591eb 100644
--- a/src/identifier.cpp
+++ b/src/identifier.cpp
@@ -62,22 +62,17 @@ bool is_ascii_letter_or_digit(char c) {
          (c >= '0' && c <= '9');
 }
 
-bool valid_name_code_point(std::string_view input, bool first) {
-  // https://urlpattern.spec.whatwg.org/#is-a-valid-name-code-point
-  if (input.empty()) {
-    return false;
-  }
+bool valid_name_code_point(char32_t code_point, bool first) {
   // https://tc39.es/ecma262/#prod-IdentifierStart
   // Fast paths:
   if (first &&
-      (input[0] == '$' || input[0] == '_' || is_ascii_letter(input[0]))) {
+      (code_point == '$' || code_point == '_' || is_ascii_letter(code_point))) {
     return true;
   }
-  if (!first && (input[0] == '$' || is_ascii_letter_or_digit(input[0]))) {
+  if (!first && (code_point == '$' || is_ascii_letter_or_digit(code_point))) {
     return true;
   }
   // Slow path...
-  uint32_t code_point = get_first_code_point(input);
   if (code_point == 0xffffffff) {
     return false;  // minimal error handling
   }
diff --git a/tests/identifier_tests.cpp b/tests/identifier_tests.cpp
index d526986..23c5dcb 100644
--- a/tests/identifier_tests.cpp
+++ b/tests/identifier_tests.cpp
@@ -1,9 +1,24 @@
 #include <iostream>
 
-#include "ada/idna/identifier.h"
+#include "idna.h"
+
+std::u32string to_utf32(std::string_view ut8_string) {
+  size_t utf32_length =
+      ada::idna::utf32_length_from_utf8(ut8_string.data(), ut8_string.size());
+  std::u32string utf32(utf32_length, '\0');
+  size_t actual_utf32_length = ada::idna::utf8_to_utf32(
+      ut8_string.data(), ut8_string.size(), utf32.data());
+  return utf32;
+}
 
 void verify(std::string_view input, bool first, bool expected) {
-  if (ada::idna::valid_name_code_point(input, first) != expected) {
+  std::u32string first_code_point = to_utf32(input);
+  if (first_code_point.empty()) {
+    std::cerr << "bug" << input << std::endl;
+    exit(-1);
+  }
+  if (ada::idna::valid_name_code_point(first_code_point[0], first) !=
+      expected) {
     std::cerr << "bug" << input << std::endl;
     exit(-1);
   }