diff --git a/include/fmt/base.h b/include/fmt/base.h
index cbc78e2d69da..9d02f25a3204 100644
--- a/include/fmt/base.h
+++ b/include/fmt/base.h
@@ -1790,7 +1790,7 @@ template <typename T> class buffer {
 struct buffer_traits {
   constexpr explicit buffer_traits(size_t) {}
   constexpr auto count() const -> size_t { return 0; }
-  FMT_CONSTEXPR auto limit(size_t size) -> size_t { return size; }
+  constexpr auto limit(size_t size) const -> size_t { return size; }
 };
 
 class fixed_buffer_traits {
diff --git a/include/fmt/os.h b/include/fmt/os.h
index 1a047cd0d738..b2cc5e4b85ff 100644
--- a/include/fmt/os.h
+++ b/include/fmt/os.h
@@ -326,7 +326,7 @@ namespace detail {
 struct buffer_size {
   constexpr buffer_size() = default;
   size_t value = 0;
-  constexpr auto operator=(size_t val) const -> buffer_size {
+  FMT_CONSTEXPR auto operator=(size_t val) const -> buffer_size {
     auto bs = buffer_size();
     bs.value = val;
     return bs;