diff --git a/tools/codegen/core/gen_nano_proto.sh b/tools/codegen/core/gen_nano_proto.sh
index ad3c920ee0b8bb8d185ddd5dde8896ea7c6cc51e..81b91229709dc34b9b686696f8c042b89d706e14 100755
--- a/tools/codegen/core/gen_nano_proto.sh
+++ b/tools/codegen/core/gen_nano_proto.sh
@@ -96,7 +96,7 @@ if [[ ! -f "${EXPECTED_OPTIONS_FILE_PATH}" ]]; then
   exit 4
 fi
 
-mkdir -p "ABS_OUTPUT_DIR"
+mkdir -p "$ABS_OUTPUT_DIR"
 if [ $? != 0 ]; then
   echo "Error creating output directory $ABS_OUTPUT_DIR"
   exit 2