diff --git a/qemu/scripts/decodetree.py b/qemu/scripts/decodetree.py
index ab60f4d8..321487d4 100644
--- a/qemu/scripts/decodetree.py
+++ b/qemu/scripts/decodetree.py
@@ -318,7 +318,7 @@ class Field:
         return '{0}(insn, {1}, {2})'.format(extr, self.pos, self.len)
 
     def __eq__(self, other):
-        return self.sign == other.sign and self.sign == other.sign
+        return self.sign == other.sign and self.mask == other.mask
 
     def __ne__(self, other):
         return not self.__eq__(other)