diff --git a/scripts/mksystemimg.sh b/scripts/mksystemimg.sh
index 93bc6f7..a26c98b 100755
--- a/scripts/mksystemimg.sh
+++ b/scripts/mksystemimg.sh
@@ -1,4 +1,5 @@
 #!/bin/sh
 
-rm -f system.img
-mklittlefs -c system -b 512 -s $((1<<20)) system.img
+if [ ! -e system.img ]; then
+  mklittlefs -c system -b 512 -s $((1<<20)) system.img
+fi