diff --git a/services/lib/docker/build_sources.sh b/services/lib/docker/build_sources.sh
--- a/services/lib/docker/build_sources.sh
+++ b/services/lib/docker/build_sources.sh
@@ -13,7 +13,7 @@
 
 pushd cmake/build
 cmake ../..
-make -j $NPROC
+make -j "$NPROC"
 
 popd