diff --git a/.dockerignore b/.dockerignore
index 9794174..0424638 100644
--- a/.dockerignore
+++ b/.dockerignore
@@ -2,6 +2,9 @@
 # (data, backups, .env, files a deploy tool adds) stays out of the build,
 # so it can't bloat the upload or change while it's being sent.
 *
+# Build tools may add their own copy of the Dockerfile (Arcane writes
+# .arcane.external.Dockerfile), which has to reach the builder.
+!*Dockerfile*
 !go.mod
 !go.sum
 !cmd/