diff --git a/examples/simple/custom_option.py b/examples/simple/custom_option.py
index a8b4e7789..324d27e7c 100644
--- a/examples/simple/custom_option.py
+++ b/examples/simple/custom_option.py
@@ -7,4 +7,5 @@ def start(options):
 
 
 def configure(options, updated):
-    ctx.log.info("custom option value: %s" % options.custom)
+    if "custom" in updated:
+        ctx.log.info("custom option value: %s" % options.custom)
diff --git a/mitmproxy/optmanager.py b/mitmproxy/optmanager.py
index 225a2f739..495354f4c 100644
--- a/mitmproxy/optmanager.py
+++ b/mitmproxy/optmanager.py
@@ -81,8 +81,6 @@ class _Option:
 class OptManager:
     """
         OptManager is the base class from which Options objects are derived.
-        Note that the __init__ method of all child classes must force all
-        arguments to be positional only, by including a "*" argument.
 
         .changed is a blinker Signal that triggers whenever options are
         updated. If any handler in the chain raises an exceptions.OptionsError
@@ -176,15 +174,29 @@ class OptManager:
             o.reset()
         self.changed.send(self._options.keys())
 
+    def update_known(self, **kwargs):
+        """
+            Update and set all known options from kwargs. Returns a dictionary
+            of unknown options.
+        """
+        known, unknown = {}, {}
+        for k, v in kwargs.items():
+            if k in self._options:
+                known[k] = v
+            else:
+                unknown[k] = v
+        updated = set(known.keys())
+        if updated:
+            with self.rollback(updated):
+                for k, v in known.items():
+                    self._options[k].set(v)
+                self.changed.send(self, updated=updated)
+        return unknown
+
     def update(self, **kwargs):
-        updated = set(kwargs.keys())
-        with self.rollback(updated):
-            for k, v in kwargs.items():
-                if k not in self._options:
-                    raise KeyError("No such option: %s" % k)
-                self._options[k].set(v)
-            self.changed.send(self, updated=updated)
-        return self
+        u = self.update_known(**kwargs)
+        if u:
+            raise KeyError("Unknown options: %s" % ", ".join(u.keys()))
 
     def setter(self, attr):
         """
@@ -413,12 +425,11 @@ def load(opts, text):
     """
         Load configuration from text, over-writing options already set in
         this object. May raise OptionsError if the config file is invalid.
+
+        Returns a dictionary of all unknown options.
     """
     data = parse(text)
-    try:
-        opts.update(**data)
-    except KeyError as v:
-        raise exceptions.OptionsError(v)
+    return opts.update_known(**data)
 
 
 def load_paths(opts, *paths):
@@ -426,18 +437,22 @@ def load_paths(opts, *paths):
         Load paths in order. Each path takes precedence over the previous
         path. Paths that don't exist are ignored, errors raise an
         OptionsError.
+
+        Returns a dictionary of unknown options.
     """
+    ret = {}
     for p in paths:
         p = os.path.expanduser(p)
         if os.path.exists(p) and os.path.isfile(p):
             with open(p, "r") as f:
                 txt = f.read()
             try:
-                load(opts, txt)
+                ret.update(load(opts, txt))
             except exceptions.OptionsError as e:
                 raise exceptions.OptionsError(
                     "Error reading %s: %s" % (p, e)
                 )
+    return ret
 
 
 def serialize(opts, text, defaults=False):
diff --git a/mitmproxy/tools/main.py b/mitmproxy/tools/main.py
index 8210580cf..35567b620 100644
--- a/mitmproxy/tools/main.py
+++ b/mitmproxy/tools/main.py
@@ -69,10 +69,13 @@ def run(MasterKlass, args):  # pragma: no cover
     args = parser.parse_args(args)
     master = None
     try:
-        optmanager.load_paths(opts, args.conf)
+        unknown = optmanager.load_paths(opts, args.conf)
         server = process_options(parser, opts, args)
         master = MasterKlass(opts, server)
         master.addons.configure_all(opts, opts.keys())
+        remaining = opts.update_known(**unknown)
+        if remaining and opts.verbosity > 1:
+            print("Ignored options: %s" % remaining)
         if args.options:
             print(optmanager.dump_defaults(opts))
             sys.exit(0)
diff --git a/test/mitmproxy/test_optmanager.py b/test/mitmproxy/test_optmanager.py
index 012c463c9..df3928290 100644
--- a/test/mitmproxy/test_optmanager.py
+++ b/test/mitmproxy/test_optmanager.py
@@ -83,10 +83,11 @@ def test_options():
 
     with pytest.raises(TypeError):
         TO(nonexistent = "value")
-    with pytest.raises(Exception, match="No such option"):
+    with pytest.raises(Exception, match="Unknown options"):
         o.nonexistent = "value"
-    with pytest.raises(Exception, match="No such option"):
+    with pytest.raises(Exception, match="Unknown options"):
         o.update(nonexistent = "value")
+    assert o.update_known(nonexistent = "value") == {"nonexistent": "value"}
 
     rec = []
 
@@ -226,9 +227,7 @@ def test_serialize():
 
     t = ""
     optmanager.load(o2, t)
-
-    with pytest.raises(exceptions.OptionsError, matches='No such option: foobar'):
-        optmanager.load(o2, "foobar: '123'")
+    assert optmanager.load(o2, "foobar: '123'") == {"foobar": "123"}
 
 
 def test_serialize_defaults():
@@ -252,7 +251,11 @@ def test_saving(tmpdir):
 
     with open(dst, 'a') as f:
         f.write("foobar: '123'")
-    with pytest.raises(exceptions.OptionsError, matches=''):
+    assert optmanager.load_paths(o, dst) == {"foobar": "123"}
+
+    with open(dst, 'a') as f:
+        f.write("'''")
+    with pytest.raises(exceptions.OptionsError):
         optmanager.load_paths(o, dst)