diff --git a/iverilog.conf b/iverilog.conf
index 4c531bec9..372c07a6f 100644
--- a/iverilog.conf
+++ b/iverilog.conf
@@ -66,10 +66,10 @@
 # These rules support synthesized and non-synthesized variants.
 
 [-tvvp -S]
-<ivl>%B/ivl %W %[s-s%s] %[N-N%N] %[T-T%T] -tdll -fDLL=%B/vvp.tgt -Fsynth -Fsyn-rules -Fcprop -Fnodangle %f %m -- -
+<ivl>%B/ivl %W %[s-s%s] %[N-N%N] %[T-T%T] -tdll -fDLL=%B/vvp.tgt -Fsynth -Fsyn-rules -Fcprop -Fnodangle %f %m -o%o -- -
 
 [-tvvp]
-<ivl>%B/ivl %W %[s-s%s] %[N-N%N] %[T-T%T] -tdll -fDLL=%B/vvp.tgt -Fcprop -Fnodangle %f %m -- -
+<ivl>%B/ivl %W %[s-s%s] %[N-N%N] %[T-T%T] -tdll -fDLL=%B/vvp.tgt -Fcprop -Fnodangle %f %m -o%o -- -
 
 # --
 # The vvm target uses the <ivl> string to take the preprocessed code from