diff --git a/src/commandline.cpp b/src/commandline.cpp
index 4d55418..64ac03e 100644
--- a/src/commandline.cpp
+++ b/src/commandline.cpp
@@ -37,7 +37,13 @@ namespace duck {
 		all.add(desc).add(positional_options);
 		po::positional_options_description pd;
 		pd.add("input-url", 1).add("xpath", 1);
-		po::store(po::command_line_parser(parArgc, parArgv).options(all).positional(pd).run(), parVarMap);
+		try {
+			po::store(po::command_line_parser(parArgc, parArgv).options(all).positional(pd).run(), parVarMap);
+		}
+		catch (const po::unknown_option& err) {
+			throw std::invalid_argument(err.what());
+		}
+
 		po::notify(parVarMap);
 
 		if (parVarMap.count("help")) {