diff --git a/mozilla/extensions/python/xpcom/client/__init__.py b/mozilla/extensions/python/xpcom/client/__init__.py
index e422dd49a17..70e784a117e 100644
--- a/mozilla/extensions/python/xpcom/client/__init__.py
+++ b/mozilla/extensions/python/xpcom/client/__init__.py
@@ -299,7 +299,11 @@ class Component(_XPCOMBase):
             self._build_all_supported_interfaces_()
             interface_name = self.__dict__['_name_to_interface_name_'].get(attr, None)
         if interface_name is not None:
-            interface = self._interface_names_[interface_name]
+            interface = self._interface_names_.get(interface_name, None)
+            if interface is None:
+                iid = XPTI_GetInterfaceInfoManager().GetInfoForName(interface_name).GetIID()
+                self.QueryInterface(iid)
+                interface = self.__dict__['_interface_names_'][interface_name]
             setattr(interface, attr, val)
             return
         raise AttributeError, "XPCOM component '%s' can not set attribute '%s'" % (self._object_name_, attr)
diff --git a/mozilla/extensions/python/xpcom/test/test_test_component.py b/mozilla/extensions/python/xpcom/test/test_test_component.py
index 8bb82eb1ab3..2f55b88bc8d 100644
--- a/mozilla/extensions/python/xpcom/test/test_test_component.py
+++ b/mozilla/extensions/python/xpcom/test/test_test_component.py
@@ -380,6 +380,12 @@ def test_all():
     c = xpcom.components.classes[contractid].createInstance()
     test_base_interface(c)
     test_derived_interface(c, test_flat=1)
+
+    # We had a bug where a "set" of an attribute before a "get" failed.
+    # Don't let it happen again :)
+    c = xpcom.components.classes[contractid].createInstance()
+    c.boolean_value = 0
+    
     # This name is used in exceptions etc - make sure we got it from nsIClassInfo OK.
     assert c._object_name_ == "Python.TestComponent"