diff --git a/cmdopt2/parser.cpp b/cmdopt2/parser.cpp
index 0f126abf..d3fbd0f6 100644
--- a/cmdopt2/parser.cpp
+++ b/cmdopt2/parser.cpp
@@ -207,13 +207,13 @@ parser::parse (int const argc, const char *const *argv)
         arg_cursor++;
     }
 
-    for (int i = 0, last = std::ssize (m_positional); i < last; ++i)
+    for (int i = 0, last = int (m_positional.size ()); i < last; ++i)
         if (m_positional[i].required () and !found_positional[i])
             throw std::runtime_error (
                 fmt::format ("Missing required position argument {}", m_positional[i].name)
             );
 
-    for (int i = 0, last = std::ssize (m_keyword); i < last; ++i)
+    for (int i = 0, last = int (m_keyword.size ()); i < last; ++i)
         if (m_keyword[i].required () and !found_keyword[i])
             throw std::runtime_error (
                 fmt::format ("Missing required named argument {}", m_keyword[i].name)