diff --git a/nix/t1/verilated.nix b/nix/t1/verilated.nix
index 4c27f9f8b..498c2ea9b 100644
--- a/nix/t1/verilated.nix
+++ b/nix/t1/verilated.nix
@@ -24,7 +24,7 @@ stdenv.mkDerivation {
       ${lib.optionalString enable-trace "--trace-fst"} \
       --timing \
       --threads 8 \
-      -O3 \
+      -O1 \
       --cc TestBench
 
     echo "[nix] building verilated C lib"