diff --git a/backends/smt2/smtio.py b/backends/smt2/smtio.py
index ab20a4af2..cea0fc56c 100644
--- a/backends/smt2/smtio.py
+++ b/backends/smt2/smtio.py
@@ -1023,6 +1023,8 @@ class MkVcd:
         assert t >= self.t
         if t != self.t:
             if self.t == -1:
+                print("$version Generated by Yosys-SMTBMC $end", file=self.f)
+                print("$timescale 1ns $end", file=self.f)
                 print("$var integer 32 t smt_step $end", file=self.f)
                 print("$var event 1 ! smt_clock $end", file=self.f)