diff --git a/bin/primes.py b/bin/primes.py
index 0e63b3440..f8f671dc6 100755
--- a/bin/primes.py
+++ b/bin/primes.py
@@ -47,6 +47,19 @@ class AgoraCmd(click.Command):
         - Visit anagora.org/foo/1 to execute e.g. <bin/foo.py 1>, <exec/foo.py 1> from your garden.")
         """)
 
+    def __call__(self, *args, **kwargs):
+        try:
+            return super(ShowUsageOnMissingError, self).__call__(
+                *args, standalone_mode=False, **kwargs)
+        except click.MissingParameter as exc:
+            exc.ctx = None
+            exc.show(file=sys.stdout)
+            click.echo()
+            try:
+                super(ShowUsageOnMissingError, self).__call__(['--help'])
+            except SystemExit:
+                sys.exit(exc.exit_code)
+
 @click.command(cls=AgoraCmd)
 @click.argument('n', type=click.INT)
 def prime(n):