diff --git a/scripts/decodetree.py b/scripts/decodetree.py
index 6e7ba278be..f6f58e2fec 100755
--- a/scripts/decodetree.py
+++ b/scripts/decodetree.py
@@ -589,7 +589,7 @@ def parse_generic(lineno, is_format, name, toks):
             continue
 
         # 'Foo=number' sets an argument field to a constant value
-        if re_fullmatch(re_ident + '=[0-9]+', t):
+        if re_fullmatch(re_ident + '=[+-]?[0-9]+', t):
             (fname, value) = t.split('=')
             value = int(value)
             flds = add_field(lineno, flds, fname, ConstField(value))