diff --git a/src/py65/monitor.py b/src/py65/monitor.py
index 80966aa..8007301 100644
--- a/src/py65/monitor.py
+++ b/src/py65/monitor.py
@@ -566,8 +566,7 @@ class Monitor(cmd.Cmd):
     def do_fill(self, args):
         split = shlex.split(args)
         if len(split) < 2:
-            self._output("Syntax error: %s" % args)
-            return
+            return self.help_fill()
 
         start, end = self._address_parser.range(split[0])
         filler = map(self._address_parser.number, split[1:])
diff --git a/src/py65/tests/test_monitor.py b/src/py65/tests/test_monitor.py
index 110fcf1..f8ec3dd 100644
--- a/src/py65/tests/test_monitor.py
+++ b/src/py65/tests/test_monitor.py
@@ -291,7 +291,7 @@ class MonitorTests(unittest.TestCase):
         mon.do_help('f')
 
         out = stdout.getvalue()
-        self.assertTrue(out.startswith('fill'))
+        self.assertTrue(out.startswith('fill <address_range>'))
 
     def test_shortcut_gt_for_fill(self):
         stdout = StringIO()
@@ -299,7 +299,24 @@ class MonitorTests(unittest.TestCase):
         mon.do_help('>')
 
         out = stdout.getvalue()
-        self.assertTrue(out.startswith('fill'))
+        self.assertTrue(out.startswith('fill <address_range>'))
+
+    def test_help_fill(self):
+        stdout = StringIO()
+        mon = Monitor(stdout=stdout)
+        mon.help_fill()
+
+        out = stdout.getvalue()
+        self.assertTrue(out.startswith('fill <address_range>'))
+
+    def test_do_fill_with_no_args_shows_help(self):
+        stdout = StringIO()
+        mon = Monitor(stdout=stdout)
+        mon.do_fill('')
+
+        out = stdout.getvalue()
+        self.assertTrue(out.startswith('fill <address_range>'))
+
 
     # goto