Index: libcxx/include/__chrono/formatter.h
===================================================================
--- libcxx/include/__chrono/formatter.h
+++ libcxx/include/__chrono/formatter.h
@@ -85,7 +85,8 @@
 
   using __duration = chrono::duration<_Rep, _Period>;
 
-  auto __fraction = __value - chrono::duration_cast<chrono::seconds>(__value);
+  constexpr auto __one_sec = chrono::duration_cast<chrono::microseconds>(chrono::seconds(1u));
+  auto __micro_seconds = chrono::duration_cast<chrono::microseconds>(__value).count() % __one_sec.count();
   if constexpr (chrono::treat_as_floating_point_v<_Rep>)
     // When the floating-point value has digits itself they are ignored based
     // on the wording in [tab:time.format.spec]
@@ -100,13 +101,13 @@
     // differently and uses 3 decimals.
     // https://godbolt.org/z/6dsbnW8ba
     std::format_to(std::ostreambuf_iterator<_CharT>{__sstr},
-                   _LIBCPP_STATICALLY_WIDEN(_CharT, "{:0{}.0f}"),
-                   __fraction.count(),
+                   _LIBCPP_STATICALLY_WIDEN(_CharT, "{:{}.0f}"),
+                   __micro_seconds,
                    chrono::hh_mm_ss<__duration>::fractional_width);
   else
     std::format_to(std::ostreambuf_iterator<_CharT>{__sstr},
-                   _LIBCPP_STATICALLY_WIDEN(_CharT, "{:0{}}"),
-                   __fraction.count(),
+                   _LIBCPP_STATICALLY_WIDEN(_CharT, "{:0<{}}"),
+                   __micro_seconds,
                    chrono::hh_mm_ss<__duration>::fractional_width);
 }