diff --git a/tools/boot/ci-qemu-test.sh b/tools/boot/ci-qemu-test.sh
index b2a6cb5ab9f5..8d46182332b5 100755
--- a/tools/boot/ci-qemu-test.sh
+++ b/tools/boot/ci-qemu-test.sh
@@ -95,7 +95,7 @@ trap tempdir_cleanup EXIT SIGINT SIGHUP SIGTERM SIGQUIT
 ( cd ${SRCTOP} && tempdir_setup )
 
 # And, boot in QEMU.
-: ${BOOTLOG:=${TMPDIR}/ci-qemu-test-boot.log}
+: ${BOOTLOG:=${TMPDIR:-/tmp}/ci-qemu-test-boot.log}
 timeout 300 \
     qemu-system-x86_64 -m 256M -bios ${OVMF} \
         -serial stdio -vga none -nographic -monitor none \