diff --git a/PythonicGcodeMachine/Gcode/Rs274/Ast.py b/PythonicGcodeMachine/Gcode/Rs274/Ast.py
index 963964cb351a378e138fc0b50de5d7bf5f9bcdeb..7d492984652110c6ba7325f04e3ba43614b7f608 100644
--- a/PythonicGcodeMachine/Gcode/Rs274/Ast.py
+++ b/PythonicGcodeMachine/Gcode/Rs274/Ast.py
@@ -563,7 +563,12 @@ class Word(LineItem):
 
     def ansi_str(self):
 
-        if self._letter in 'GM':
+        if self._machine:
+            gm = self._machine.GM_LETTERS
+        else:
+            gm = 'GM'
+
+        if self._letter in gm:
             return Line.ANSI_G(str(self))
         else:
             return Line.ANSI_X(self._letter) + Line.ANSI_VALUE(str(self._value))
@@ -577,15 +582,24 @@ class Word(LineItem):
     ##############################################
 
     @property
-    def is_valid_gcode(self):
+    def is_gm_gcode(self):
         self._check_machine()
-        return str(self) in self._machine.config.gcodes
+        return self._machine.is_gm_word(self)
+
+    ##############################################
+
+    @property
+    def is_valid_gcode(self):
+        if self.is_gm_gcode:
+            return str(self) in self._machine.config.gcodes
+        else:
+            return True
 
     ##############################################
 
     @property
     def meaning(self):
-        if self.is_valid_gcode:
+        if self.is_gm_gcode:
             return self._machine.config.gcodes[str(self)].meaning
         else:
             return self._machine.config.letters[self.letter].meaning
@@ -594,7 +608,7 @@ class Word(LineItem):
 
     @property
     def modal_group(self):
-        if self.is_valid_gcode:
+        if self.is_gm_gcode:
             return self._machine.config.modal_groups[str(self)]
         else:
             return None
@@ -603,7 +617,7 @@ class Word(LineItem):
 
     @property
     def execution_order(self):
-        if self.is_valid_gcode:
+        if self.is_gm_gcode:
             return self._machine.config.execution_order[str(self)]
         else:
             return None
diff --git a/PythonicGcodeMachine/Gcode/Rs274/Machine.py b/PythonicGcodeMachine/Gcode/Rs274/Machine.py
index 96e6939c3941baebabe489148b4330fad28b7213..1864685cb6050496468cb011df905d26b7bbde0b 100644
--- a/PythonicGcodeMachine/Gcode/Rs274/Machine.py
+++ b/PythonicGcodeMachine/Gcode/Rs274/Machine.py
@@ -40,6 +40,8 @@ class GcodeMachine:
 
     PARSER_CLS = GcodeParser
 
+    GM_LETTERS = 'GM'
+
     ##############################################
 
     def __init__(self):
@@ -85,3 +87,11 @@ class GcodeMachine:
         pass
 
     ##############################################
+
+    def is_gm_letter(self, letter):
+        return letter in self.GM_LETTERS
+
+    ##############################################
+
+    def is_gm_word(self, word):
+        return self.is_gm_letter(word.letter)
diff --git a/examples/gcode/annotate-gcode.py b/examples/gcode/annotate-gcode.py
index ab393e736e05850460584ba31e81b04d2b6aac8f..8e933df1bbb614d49d357b82f9cf3c003b9fce1b 100644
--- a/examples/gcode/annotate-gcode.py
+++ b/examples/gcode/annotate-gcode.py
@@ -69,11 +69,12 @@ for line in program:
     # print(line.ansi_str()) # Fixme: pyterate
     print(str(line))
     for word in line.iter_on_word():
-        if word.is_valid_gcode:
+        if word.is_gm_gcode:
             margin = ' '*9
             print(meaning_format.format(str(word), word.meaning))
             print(margin + 'Modal group: {}'.format(word.modal_group.meaning))
             print(margin + 'Execution order: {}'.format(word.execution_order.index))
+            print(margin + 'Valid G-code: {}'.format(word.is_valid_gcode))
         else:
             print(meaning_format.format(word.letter, word.meaning))
 #o#