diff --git a/tools/sim/Dockerfile.sim b/tools/sim/Dockerfile.sim
index 6ef0cf6915..02e59455bd 100644
--- a/tools/sim/Dockerfile.sim
+++ b/tools/sim/Dockerfile.sim
@@ -88,4 +88,4 @@ COPY ./selfdrive $HOME/openpilot/selfdrive
 COPY ./tools $HOME/openpilot/tools
 
 WORKDIR $HOME/openpilot
-RUN scons -j40
+RUN scons -j$(nproc)