diff --git a/nix/t1/vcs.nix b/nix/t1/vcs.nix
index 3b862f21f4..20d9b34279 100644
--- a/nix/t1/vcs.nix
+++ b/nix/t1/vcs.nix
@@ -24,6 +24,7 @@ stdenv.mkDerivation {
     VERDI_HOME=$("$fhsBash" -c "printenv VERDI_HOME")
     "$fhsBash" vcs \
       -sverilog \
+      -fgp \
       -full64 \
       -timescale=1ns/1ps \
       -P $VERDI_HOME/share/PLI/VCS/LINUX64/novas.tab $VERDI_HOME/share/PLI/VCS/LINUX64/pli.a \
diff --git a/tests/make-emu-result.nix b/tests/make-emu-result.nix
index 514a67bbb7..32d7ebed01 100644
--- a/tests/make-emu-result.nix
+++ b/tests/make-emu-result.nix
@@ -117,6 +117,7 @@ let
 
         RUST_BACKTRACE=full "${vcs-emu}/bin/t1-vcs-simulator" \
           --elf-file ${testCase}/bin/${testCase.pname}.elf \
+          -fgp=num_threads:7 \
           1> /dev/null \
           2> $rtlEventOutPath
 
@@ -152,6 +153,7 @@ let
         RUST_BACKTRACE=full "${vcs-emu-trace}/bin/t1-vcs-simulator" \
           --elf-file ${testCase}/bin/${testCase.pname}.elf \
           --wave-path ${testCase.pname}.fsdb \
+          -fgp=num_threads:6,num_fsdb_threads:1 \
           1> /dev/null \
           2> $rtlEventOutPath