diff --git a/loopy/kernel/instruction.py b/loopy/kernel/instruction.py
index 1e5c36fcf4bc5c8a1fa71f59d088d2612310f36a..90be2f409fa9fb1e363df8f56d62d7d9e8e4e54f 100644
--- a/loopy/kernel/instruction.py
+++ b/loopy/kernel/instruction.py
@@ -440,7 +440,8 @@ class InstructionBase(ImmutableRecord):
 
         from loopy.tools import intern_frozenset_of_ids
 
-        self.id = intern(self.id)
+        if self.id is not None:
+            self.id = intern(self.id)
         self.depends_on = intern_frozenset_of_ids(self.depends_on)
         self.groups = intern_frozenset_of_ids(self.groups)
         self.conflicts_with_groups = (