diff --git a/include/fmt/chrono.h b/include/fmt/chrono.h
index 07115c5c..682efd8d 100644
--- a/include/fmt/chrono.h
+++ b/include/fmt/chrono.h
@@ -558,12 +558,14 @@ inline void write_digit2_separated(char* buf, unsigned a, unsigned b,
   auto usep = static_cast<unsigned long long>(sep);
   // Add ASCII '0' to each digit byte and insert separators.
   digits |= 0x3030003030003030 | (usep << 16) | (usep << 40);
+
+  constexpr const size_t len = 8;
   if (const_check(is_big_endian())) {
-    char tmp[8];
-    memcpy(tmp, &digits, 8);
-    std::reverse_copy(tmp, tmp + 8, buf);
+    char tmp[len];
+    memcpy(tmp, &digits, len);
+    std::reverse_copy(tmp, tmp + len, buf);
   } else {
-    memcpy(buf, &digits, 8);
+    memcpy(buf, &digits, len);
   }
 }