diff --git a/include/gsl/multi_span b/include/gsl/multi_span
index dbca3a4..6ffd624 100644
--- a/include/gsl/multi_span
+++ b/include/gsl/multi_span
@@ -1052,7 +1052,7 @@ struct dim_t<dynamic_range>
 {
     static const std::ptrdiff_t value = dynamic_range;
     const std::ptrdiff_t dvalue;
-    dim_t(std::ptrdiff_t size) : dvalue(size) {}
+    constexpr dim_t(std::ptrdiff_t size) GSL_NOEXCEPT : dvalue(size) {}
 };
 
 template <std::ptrdiff_t N, class = std::enable_if_t<(N >= 0)>>