--- a/src/utils/view.hh
+++ b/src/utils/view.hh
@@ -206,6 +206,7 @@ public:
 	}
 
 	[[nodiscard]] constexpr friend difference_type operator-(const TransformIterator& x, const TransformIterator& y)
+	requires std::sized_sentinel_for<Iterator, Iterator>
 	{
 		return x.it - y.it;
 	}