diff --git a/migen/fhdl/structure.py b/migen/fhdl/structure.py
index 8052fdffb..350670fc5 100644
--- a/migen/fhdl/structure.py
+++ b/migen/fhdl/structure.py
@@ -89,10 +89,16 @@ class Value(HUID):
 	
 	def __getitem__(self, key):
 		if isinstance(key, int):
+			if (key < 0):
+				key += len(self)
 			return _Slice(self, key, key+1)
 		elif isinstance(key, slice):
 			start = key.start or 0
 			stop = key.stop or len(self)
+			if (start < 0):
+				start += len(self)
+			if (stop < 0):
+				stop += len(self)
 			if stop > len(self):
 				stop = len(self)
 			if key.step != None: