diff --git a/include/fmt/base.h b/include/fmt/base.h
index 72942615..70f18c23 100644
--- a/include/fmt/base.h
+++ b/include/fmt/base.h
@@ -1809,8 +1809,7 @@ template <typename T> class buffer {
   /// Appends data to the end of the buffer.
   template <typename U>
   FMT_CONSTEXPR20 void append(const U* begin, const U* end) {
-    static_assert(std::is_same<T, U>::value || std::is_same<U, char>::value,
-                  "U must be T or char to prevent static_cast overflow");
+    static_assert(std::is_same<T, U>() || std::is_same<U, char>(), "");
     while (begin != end) {
       auto size = size_;
       auto free_cap = capacity_ - size;