diff --git a/include/fmt/chrono.h b/include/fmt/chrono.h
index 77a7a37f..ad15be74 100644
--- a/include/fmt/chrono.h
+++ b/include/fmt/chrono.h
@@ -451,7 +451,9 @@ FMT_END_DETAIL_NAMESPACE
 template <typename Char, typename Duration>
 struct formatter<std::chrono::time_point<std::chrono::system_clock, Duration>,
                  Char> : formatter<std::tm, Char> {
-  FMT_CONSTEXPR formatter() { this->specs = {default_specs, 17}; }
+  FMT_CONSTEXPR formatter() {
+    this->specs = {default_specs, sizeof(default_specs) / sizeof(Char)};
+  }
 
   template <typename ParseContext>
   FMT_CONSTEXPR auto parse(ParseContext& ctx) -> decltype(ctx.begin()) {