diff --git a/sim/run.py b/sim/run.py
index 3f63043..c743fd4 100644
--- a/sim/run.py
+++ b/sim/run.py
@@ -177,6 +177,7 @@ def __init__(self, dirname):
 
     # Create VUnit object from command line arguments
     vu = VUnit.from_args(args=args)
+    vu.add_vhdl_builtins()
 
     # Create test suite
     create_test_suite(vu, args)