diff --git a/tests/scripts/all.sh b/tests/scripts/all.sh
index f30795c..aeca888 100755
--- a/tests/scripts/all.sh
+++ b/tests/scripts/all.sh
@@ -175,7 +175,7 @@
 
     # if MAKEFLAGS is not set add the -j option to speed up invocations of make
     if [ -z "${MAKEFLAGS+set}" ]; then
-        export MAKEFLAGS="-j"
+        export MAKEFLAGS="-j$(all_sh_nproc)"
     fi
 
     # Include more verbose output for failing tests run by CMake
@@ -343,6 +343,18 @@
 trap 'fatal_signal INT' INT
 trap 'fatal_signal TERM' TERM
 
+# Number of processors on this machine. Used as the default setting
+# for parallel make.
+all_sh_nproc ()
+{
+    {
+        nproc || # Linux
+        sysctl -n hw.ncpuonline || # NetBSD, OpenBSD
+        sysctl -n hw.ncpu || # FreeBSD
+        echo 1
+    } 2>/dev/null
+}
+
 msg()
 {
     if [ -n "${current_component:-}" ]; then