diff --git a/hyper.h b/hyper.h
index fe090622..77843c0d 100644
--- a/hyper.h
+++ b/hyper.h
@@ -49,6 +49,7 @@ using std::unique_ptr;
 using std::abs;
 using std::isfinite;
 using std::isnan;
+using std::isinf;
 using std::log;
 using std::exp;
 using std::sin;