diff --git a/tests/qemu-iotests/common.rc b/tests/qemu-iotests/common.rc
index 10d83d8361..c0f8f0f8df 100644
--- a/tests/qemu-iotests/common.rc
+++ b/tests/qemu-iotests/common.rc
@@ -1008,7 +1008,7 @@ _require_disk_usage()
     else
         FILENAME="$TEST_IMG_FILE"
     fi
-    if [ -e "FILENAME" ]; then
+    if [ -e "$FILENAME" ]; then
         echo "unwilling to overwrite existing file"
         exit 1
     fi