diff --git a/src/python/m5/simulate.py b/src/python/m5/simulate.py
index 682104c26f..a3ca77af1a 100644
--- a/src/python/m5/simulate.py
+++ b/src/python/m5/simulate.py
@@ -57,8 +57,8 @@ from m5.internal.stats import updateEvents as updateStatEvents
 from util import fatal
 from util import attrdict
 
-# define a MaxTick parameter
-MaxTick = 2**63 - 1
+# define a MaxTick parameter, unsigned 64 bit
+MaxTick = 2**64 - 1
 
 _memory_modes = {
     "atomic" : objects.params.atomic,