diff --git a/src/unicode.cpp b/src/unicode.cpp
index c6100dd0f..b3f6d75cf 100644
--- a/src/unicode.cpp
+++ b/src/unicode.cpp
@@ -373,8 +373,8 @@ unsigned constexpr convert_hex_to_binary(const char c) noexcept {
   if (c <= '9') {
     return c - '0';
   }
-  char del = c >= 'a' ? 'a' : 'A';
-  return 10 + (c - del);
+  char del = (c >= 'a' ? 'a' : 'A') - 10;
+  return c - del;
 }
 
 std::string percent_decode(const std::string_view input, size_t first_percent) {