diff --git a/Lib/optparse.py b/Lib/optparse.py
index 3792e76..2511595 100644
--- a/Lib/optparse.py
+++ b/Lib/optparse.py
@@ -797,7 +797,7 @@
             parser.print_version()
             parser.exit()
         else:
-            raise RuntimeError("unknown action %r" % self.action)
+            raise ValueError("unknown action %r" % self.action)
 
         return 1