diff --git a/loopy/kernel/data.py b/loopy/kernel/data.py
index 5af3f0272073243417c3111a847b921a41afec6e..cfbff7a30459f869d902c2e24afb88389d4c3ec2 100644
--- a/loopy/kernel/data.py
+++ b/loopy/kernel/data.py
@@ -1256,8 +1256,10 @@ class Assignment(MultiAssignmentBase):
     # }}}
 
     def __str__(self):
-        result = "%s: %s <- %s" % (self.id,
-                self.assignee, self.expression)
+        result = "%s <- %s" % (self.assignee, self.expression)
+
+        if self.id is not None:
+            result = "%s: " % self.id + result
 
         options = self.get_str_options()
         if options: