diff --git a/README.md b/README.md
index d3c8452..d9a574f 100644
--- a/README.md
+++ b/README.md
@@ -64,13 +64,13 @@ Apple Developer account.
 `builder.Dockerfile` bakes the pipeline's build-step dependencies
 (Go + git/make/zip/curl/jq and the X11/GL/ALSA dev libraries needed by
 the cgo `linux-x64` build) into
-`git.teletypegames.org/internal/ebitengine-builder`. Debian-based so
+`git.teletypegames.org/build/ebitengine-builder`. Debian-based so
 the linux binary links against glibc:
 
 ```sh
 docker build --platform linux/amd64 -f builder.Dockerfile \
-  -t git.teletypegames.org/internal/ebitengine-builder:latest .
-docker push git.teletypegames.org/internal/ebitengine-builder:latest
+  -t git.teletypegames.org/build/ebitengine-builder:latest .
+docker push git.teletypegames.org/build/ebitengine-builder:latest
 ```
 
 Detailed documentation lives on the wiki: `/development/ebitengine`.
diff --git a/builder.Dockerfile b/builder.Dockerfile
index 716cb09..87762bc 100644
--- a/builder.Dockerfile
+++ b/builder.Dockerfile
@@ -8,8 +8,8 @@
 #
 # Build & push (the CI runner is linux/amd64):
 #   docker build --platform linux/amd64 -f builder.Dockerfile \
-#     -t git.teletypegames.org/internal/ebitengine-builder:latest .
-#   docker push git.teletypegames.org/internal/ebitengine-builder:latest
+#     -t git.teletypegames.org/build/ebitengine-builder:latest .
+#   docker push git.teletypegames.org/build/ebitengine-builder:latest
 
 # 1.26 covers every current game repo's go.mod directive (1.25.x, 1.26.x).
 FROM golang:1.26-bookworm
@@ -24,6 +24,19 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
         libasound2-dev \
     && rm -rf /var/lib/apt/lists/*
 
+# linux-arm64 cross-build (Raspberry Pi, Odroid, retro handhelds). Ebitengine
+# needs cgo on Linux, so the arm64 target needs a cross gcc plus the same
+# X11/GL/ALSA headers for arm64. Debian's main mirror carries arm64, so
+# `dpkg --add-architecture` is enough — no ports repository needed.
+RUN dpkg --add-architecture arm64 \
+    && apt-get update && apt-get install -y --no-install-recommends \
+        gcc-aarch64-linux-gnu libc6-dev-arm64-cross \
+        libgl1-mesa-dev:arm64 libglu1-mesa-dev:arm64 \
+        libx11-dev:arm64 libxcursor-dev:arm64 libxi-dev:arm64 \
+        libxinerama-dev:arm64 libxrandr-dev:arm64 libxxf86vm-dev:arm64 \
+        libasound2-dev:arm64 \
+    && rm -rf /var/lib/apt/lists/*
+
 # Our own Go modules (engines/inkwell, engines/gorpg) are served by the forge,
 # not by proxy.golang.org, and are absent from the public checksum database.
 ENV GOPRIVATE=git.teletypegames.org