diff --git a/coverage.sh b/coverage.sh
index fcdc8a9..c056199 100755
--- a/coverage.sh
+++ b/coverage.sh
@@ -12,7 +12,10 @@ rm -f shared/cover_db.img
 # prepare image for cover_db
 guestfish -N shared/cover_db.img=disk:100M -- mkfs vfat /dev/sda
 
-cp mmdebstrap shared
+# only copy if necessary
+if [ ! -e shared/mmdebstrap ] || [ mmdebstrap -nt shared/mmdebstrap ]; then
+	cp -a mmdebstrap shared
+fi
 
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 total=54