diff --git a/build.sh b/build.sh
index acc2395..2d5393c 100755
--- a/build.sh
+++ b/build.sh
@@ -6,6 +6,13 @@
 source util.sh
 cd build
 
+# Number of processor core
+if [[ $(uname) == "OpenBSD" ]]; then
+  cores=$(sysctl -n hw.ncpu)
+else
+  cores=$(nproc)
+fi
+
 echo "$TAG Compiling binutils (usually 5-10 minutes)..."
 run_quietly giteapc-build.log \
-make -j$(nproc)
+make -j"$cores"