diff --git a/openlane/scripts/pyosys/synthesize.py b/openlane/scripts/pyosys/synthesize.py
index f5f110ff..75598f07 100644
--- a/openlane/scripts/pyosys/synthesize.py
+++ b/openlane/scripts/pyosys/synthesize.py
@@ -378,7 +378,7 @@ def run_strategy(d):
     if config["SYNTH_HIERARCHY_MODE"] == "deferred_flatten":
         # Resynthesize, flattening
         d_flat = ys.Design()
-        d_flat.add_blackbox_models(blackbox_models)
+        d_flat.add_blackbox_models(blackbox_models, includes=includes, defines=defines)
 
         shutil.copy(output, f"{output}.hierarchy.nl.v")
         d_flat.run_pass("read_verilog", "-sv", output)