diff --git a/src/arch/isa_parser.py b/src/arch/isa_parser.py
index 2db7c6aa6..bd45a8313 100755
--- a/src/arch/isa_parser.py
+++ b/src/arch/isa_parser.py
@@ -128,7 +128,7 @@ class ISAParser(Grammar):
 
     # Integer literal
     def t_INTLIT(self, t):
-        r'(0x[\da-fA-F]+)|\d+'
+        r'-?(0x[\da-fA-F]+)|\d+'
         try:
             t.value = int(t.value,0)
         except ValueError: