diff --git a/include/argparse.hpp b/include/argparse.hpp
index 701cd0a..d4c3e48 100644
--- a/include/argparse.hpp
+++ b/include/argparse.hpp
@@ -859,7 +859,7 @@ public:
    * Used in conjuction with Argument.operator== e.g., parser["foo"] == true
    * @throws std::logic_error in case of an invalid argument name
    */
-  Argument &operator[](std::string_view aArgumentName) {
+  Argument &operator[](std::string_view aArgumentName) const {
     auto tIterator = mArgumentMap.find(aArgumentName);
     if (tIterator != mArgumentMap.end()) {
       return *(tIterator->second);