diff --git a/src/util/span.hpp b/src/util/span.hpp
index a9ab79b2..7c97f5ac 100644
--- a/src/util/span.hpp
+++ b/src/util/span.hpp
@@ -15,7 +15,7 @@ namespace util {
 
         const T& at(size_t index) const {
             if (index >= length) {
-                throw std::out_of_range();
+                throw std::out_of_range("index is out of range");
             }
             return ptr[index];
         }