diff --git a/scripts/upgrade.sh b/scripts/upgrade.sh
index 65a4fc0a..b2999f80 100644
--- a/scripts/upgrade.sh
+++ b/scripts/upgrade.sh
@@ -44,7 +44,7 @@ export CCACHE_DISABLE=1
 cd ${bindir}/${repo}
 rm -f CMakeCache.txt
 memory=$(cat /proc/meminfo | grep MemAvailable | awk '{print $2}')
-let "cpuNumber = memory / 2100000"
+let "cpuNumber = memory / 2100000" || cpuNumber=1
 cmake -DCMAKE_BUILD_TYPE=Release ${srcdir}/${repo}
 make -j ${cpuNumber} fift validator-engine lite-client pow-miner validator-engine-console generate-random-id dht-server func tonlibjson rldp-http-proxy
 systemctl restart validator