diff --git a/pygcode/gcodes.py b/pygcode/gcodes.py
index f10186a..9a4f5ce 100644
--- a/pygcode/gcodes.py
+++ b/pygcode/gcodes.py
@@ -253,6 +253,16 @@ class GCode(object):
             key=key
         ))
 
+    def __setattr__(self, key, value):
+        if key in self.param_letters:
+            if key in self.params:
+                self.params[key].value = value
+            else:
+                self.add_parameter(Word(key, value))
+
+        else:
+            self.__dict__[key] = value
+
     @property
     def description(self):
         return self.__doc__
diff --git a/pygcode/words.py b/pygcode/words.py
index 776859f..df0d6b9 100644
--- a/pygcode/words.py
+++ b/pygcode/words.py
@@ -275,6 +275,11 @@ class Word(object):
             return self._value_class(self._value_str)
         return self._value
 
+    @value.setter
+    def value(self, new_value):
+        self._value = self._value_class(new_value)
+        self._value_str = None
+
     # Order
     def __lt__(self, other):
         return self.letter < other.letter