diff --git a/script/ember.sh b/script/ember.sh
index 50c7c68e75..4029d3ef52 100755
--- a/script/ember.sh
+++ b/script/ember.sh
@@ -3,7 +3,7 @@ set -ue
 
 export FASTBOOT_DISABLED
 
-if [ -z "${USE_FASTBOOT}" ]; then
+if [ -z "${USE_FASTBOOT-}" ]; then
     unset FASTBOOT_DISABLED
 else
     FASTBOOT_DISABLED=1
diff --git a/script/start-web.sh b/script/start-web.sh
index dce52263cd..bcf62b29ef 100755
--- a/script/start-web.sh
+++ b/script/start-web.sh
@@ -1,7 +1,7 @@
 #! /bin/bash
 set -ue
 
-if [[ -z "${USE_FASTBOOT}" ]]; then
+if [[ -z "${USE_FASTBOOT-}" ]]; then
     unset USE_FASTBOOT
     bin/start-nginx ./target/release/server
 else