diff --git a/mitmproxy/optmanager.py b/mitmproxy/optmanager.py
index cbf656f57..713a0b626 100644
--- a/mitmproxy/optmanager.py
+++ b/mitmproxy/optmanager.py
@@ -53,6 +53,15 @@ class OptManager(metaclass=_DefaultsMeta):
         # ._initialized = True as the final operation.
         instance = super().__new__(cls)
         instance.__dict__["_opts"] = {}
+
+        defaults = {}
+        for klass in reversed(inspect.getmro(cls)):
+            for p in inspect.signature(klass.__init__).parameters.values():
+                if p.kind in (p.KEYWORD_ONLY, p.POSITIONAL_OR_KEYWORD):
+                    if not p.default == p.empty:
+                        defaults[p.name] = p.default
+        instance.__dict__["_defaults"] = defaults
+
         return instance
 
     def __init__(self):
@@ -123,16 +132,16 @@ class OptManager(metaclass=_DefaultsMeta):
     def keys(self):
         return set(self._opts.keys())
 
+    @classmethod
+    def default(klass, opt):
+        return copy.deepcopy(klass._defaults[opt])
+
     def reset(self):
         """
             Restore defaults for all options.
         """
         self.update(**self._defaults)
 
-    @classmethod
-    def default(klass, opt):
-        return copy.deepcopy(klass._defaults[opt])
-
     def update(self, **kwargs):
         updated = set(kwargs.keys())
         for k, v in kwargs.items():
@@ -215,7 +224,7 @@ class OptManager(metaclass=_DefaultsMeta):
             snip = v.problem_mark.get_snippet()
             raise exceptions.OptionsError(
                 "Config error at line %s:\n%s\n%s" %
-                (v.problem_mark.line+1, snip, v.problem)
+                (v.problem_mark.line + 1, snip, v.problem)
             )
         if isinstance(data, str):
             raise exceptions.OptionsError("Config error - no keys found.")
diff --git a/test/mitmproxy/test_optmanager.py b/test/mitmproxy/test_optmanager.py
index 0c98daea0..97124368e 100644
--- a/test/mitmproxy/test_optmanager.py
+++ b/test/mitmproxy/test_optmanager.py
@@ -30,11 +30,6 @@ class TD2(TD):
 
 
 def test_defaults():
-    assert TD2.default("one") == "done"
-    assert TD2.default("two") == "dtwo"
-    assert TD2.default("three") == "dthree"
-    assert TD2.default("four") == "dfour"
-
     o = TD2()
     assert o._defaults == {
         "one": "done",