diff --git a/.cirrus/step-build.sh b/.cirrus/step-build.sh
index dc29271..32baf65 100755
--- a/.cirrus/step-build.sh
+++ b/.cirrus/step-build.sh
@@ -13,4 +13,9 @@
     exit 1
 fi
 
-make -j $(nproc)
+ncpu=4
+if nproc; then
+    ncpu=$(nproc)
+fi
+
+make -j ${ncpu}