diff --git a/loopy/kernel/instruction.py b/loopy/kernel/instruction.py
index 413fa1f74..76105add8 100644
--- a/loopy/kernel/instruction.py
+++ b/loopy/kernel/instruction.py
@@ -300,7 +300,7 @@ def __init__(self,
         # {{{ process happens_after/depends_on
 
         if happens_after is not None and depends_on is not None:
-            raise TypeError("may not pass both happens_after and depends_on")
+            happens_after = frozenset(happens_after) | frozenset(depends_on)
         elif depends_on is not None:
             happens_after = depends_on