diff --git a/Dockerfile b/Dockerfile
index 8c688c9..7eb5bf2 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -4,4 +4,5 @@ RUN apt-get update \
  && apt-get install --no-install-recommends --yes build-essential git gdb valgrind cmake rpm python-dev libcap-dev python-pip python-virtualenv \
  && rm -rf /var/lib/apt/lists/*
 
-RUN pip install psutil
+# Pre-install those here for faster local builds.
+RUN CFLAGS="-DPR_SET_CHILD_SUBREAPER=36 -DPR_GET_CHILD_SUBREAPER=37" pip install psutil python-prctl
diff --git a/ci/run_build.sh b/ci/run_build.sh
index ba2ba2d..74f30f9 100755
--- a/ci/run_build.sh
+++ b/ci/run_build.sh
@@ -62,9 +62,10 @@ for tini in "${BUILD_DIR}/tini" "${BUILD_DIR}/tini-static"; do
   fi
 done
 
-# Create virtual environment to run tests
+# Create virtual environment to run tests.
+# Accept system site packages for faster local builds.
 VENV="${BUILD_DIR}/venv"
-virtualenv "${VENV}"
+virtualenv --system-site-packages "${VENV}"
 
 # Don't use activate because it does not play nice with nounset
 export PATH="${VENV}/bin:${PATH}"