diff --git a/format.cc b/format.cc
index f292441f..92291c1b 100644
--- a/format.cc
+++ b/format.cc
@@ -764,7 +764,7 @@ inline Arg fmt::BasicFormatter<Char>::parse_arg_name(const Char *&s) {
   Char c;
   do {
     c = *++s;
-  } while (('a' <= c && c <= 'z') || ('A' <= c && c <= 'Z') || ('0' <= c && c <= '9'));
+  } while (is_name_start(c) || ('0' <= c && c <= '9'));
   const char *error = 0;
   Arg arg = get_arg(fmt::BasicStringRef<Char>(start, s - start), error);
   if (error)
diff --git a/test/format-test.cc b/test/format-test.cc
index 4a9e1574..5e2e153a 100644
--- a/test/format-test.cc
+++ b/test/format-test.cc
@@ -610,8 +610,9 @@ TEST(FormatterTest, ManyArgs) {
 #endif
 
 TEST(FormatterTest, NamedArg) {
+  EXPECT_EQ("1/a/A", format("{_1}/{a_}/{A_}", fmt::arg("a_", 'a'), fmt::arg("A_", "A"), fmt::arg("_1", 1)));
   char a = 'A', b = 'B', c = 'C';
-  EXPECT_EQ("BBAACC", format("{1}{b}{0}{a}{2}{c}", FMT_CAPTURE(a, b, c)));
+  EXPECT_EQ("BB/AA/CC", format("{1}{b}/{0}{a}/{2}{c}", FMT_CAPTURE(a, b, c)));
   EXPECT_EQ(" A", format("{a:>2}", FMT_CAPTURE(a)));
   EXPECT_THROW_MSG(format("{a+}", FMT_CAPTURE(a)), FormatError, "missing '}' in format string");
   EXPECT_THROW_MSG(format("{a}"), FormatError, "argument not found");