diff --git a/include/fmt/format-inl.h b/include/fmt/format-inl.h
index 1ac206a8..5fc8d2da 100644
--- a/include/fmt/format-inl.h
+++ b/include/fmt/format-inl.h
@@ -526,7 +526,7 @@ class bigint {
     FMT_ASSERT(compare(*this, other) >= 0, "");
     bigit borrow = 0;
     int i = other.exp_ - exp_;
-    for (int j = 0, n = static_cast<int>(other.bigits_.size()); j != n;
+    for (size_t j = 0, n = other.bigits_.size(); j != n;
          ++i, ++j) {
       subtract_bigits(i, other.bigits_[j], borrow);
     }