diff --git a/fmt/format.h b/fmt/format.h
index 1f19f7ce..5013b810 100644
--- a/fmt/format.h
+++ b/fmt/format.h
@@ -889,7 +889,8 @@ class ThousandsSep {
     if (++digit_index_ % 3 != 0)
       return;
     buffer -= sep_.size();
-    std::uninitialized_copy(sep_.data(), sep_.data() + sep_.size(), buffer);
+    std::uninitialized_copy(sep_.data(), sep_.data() + sep_.size(),
+                            internal::make_ptr(buffer, sep_.size()));
   }
 };