diff --git a/include/argparse.hpp b/include/argparse.hpp
index d30643a..4ac2468 100644
--- a/include/argparse.hpp
+++ b/include/argparse.hpp
@@ -1897,7 +1897,7 @@ namespace argparse
                         m_options.mutually_exclusive_group = group;
                     }
 
-                    ~ArgumentBuilder()
+                    ~ArgumentBuilder() noexcept(false)
                     {
                         if ((m_options.action == argparse::version) && m_options.help.empty())
                         {
@@ -1906,6 +1906,15 @@ namespace argparse
 
                         if (is_positional())
                         {
+                            if (m_options.mutually_exclusive_group != nullptr
+                                && (!m_options.nargs.has_value()
+                                    || (!std::holds_alternative<Nargs>(*m_options.nargs)
+                                        || (std::get<Nargs>(*m_options.nargs) != zero_or_one
+                                            && std::get<Nargs>(*m_options.nargs) != zero_or_more))))
+                            {
+                                throw option_error("mutually exclusive arguments must be optional");
+                            }
+
                             m_arguments.emplace_back(PositionalArgument(std::move(m_options)));
                         }
                         else
diff --git a/test/unittest/test_argument_parser.cpp b/test/unittest/test_argument_parser.cpp
index ec69ec7..e8a9062 100644
--- a/test/unittest/test_argument_parser.cpp
+++ b/test/unittest/test_argument_parser.cpp
@@ -350,6 +350,23 @@ TEST_CASE("ArgumentParser supports mutually exclusive groups")
     CHECK_NOTHROW(parser.add_mutually_exclusive_group());
 }
 
+TEST_CASE("Adding a positional argument to a mutually exclusive group results in error")
+{
+    auto parser = argparse::ArgumentParser();
+    auto group = parser.add_mutually_exclusive_group();
+
+    CHECK_THROWS_WITH_AS(group.add_argument("pos"), "mutually exclusive arguments must be optional", argparse::option_error);
+}
+
+TEST_CASE("Adding a non-required positional argument to a mutually exclusive group does not result in error")
+{
+    auto parser = argparse::ArgumentParser();
+    auto group = parser.add_mutually_exclusive_group();
+
+    CHECK_NOTHROW(group.add_argument("pos").nargs(argparse::zero_or_one));
+    CHECK_NOTHROW(group.add_argument("pos").nargs(argparse::zero_or_more));
+}
+
 TEST_CASE("Adding an optional argument to a mutually exclusive group does not result in error")
 {
     auto parser = argparse::ArgumentParser();