diff --git a/docker/README.md b/docker/README.md
index 150489f5..733d930b 100644
--- a/docker/README.md
+++ b/docker/README.md
@@ -154,3 +154,11 @@ docker run --rm -it \
   -v unittesting-home:/root \
   unittesting-local run_tests --tests-dir tests --pattern test_example.py
 ```
+
+## ARM hosts (Apple Silicon, arm64 Linux)
+
+On an ARM host, the launcher builds and runs a native arm64 image. The
+container installs the arm64 build of Sublime Text 4.
+
+Runs under amd64 emulation (for example `DOCKER_DEFAULT_PLATFORM=linux/amd64`)
+are not supported.
diff --git a/docker/entrypoint.sh b/docker/entrypoint.sh
index 27f260b3..07f8f11e 100644
--- a/docker/entrypoint.sh
+++ b/docker/entrypoint.sh
@@ -1,6 +1,7 @@
 #!/bin/bash
 
 echo PACKAGE = $PACKAGE
+echo ARCHITECTURE = $(uname -m)
 
 set -e
 
@@ -84,6 +85,37 @@ write_package_dependency_marker() {
     printf '%s\n' "$dependency_fingerprint" > "$DEPENDENCY_MARKER_DIR/$PACKAGE.sha256"
 }
 
+ensure_sublime_text_arch_matches() {
+    # A cache volume created on a different architecture holds a Sublime Text
+    # binary that cannot run here, and the bootstrap marker skips reinstall.
+    local binary="$HOME/sublime_text/sublime_text"
+    [ -f "$binary" ] || return 0
+
+    local expected
+    case "$(uname -m)" in
+        x86_64) expected=3e ;;
+        aarch64) expected=b7 ;;
+        *) return 0 ;;
+    esac
+
+    # e_machine field of the ELF header (low byte, little-endian).
+    local actual
+    actual=$(od -An -tx1 -j18 -N1 "$binary" | tr -d ' \n')
+    if [ "$actual" != "$expected" ]; then
+        local found
+        case "$actual" in
+            3e) found=x86_64 ;;
+            b7) found=aarch64 ;;
+            *) found="unknown (ELF machine 0x$actual)" ;;
+        esac
+        echo "Error: the cache volume has a Sublime Text build for $found," >&2
+        echo "but this container runs on $(uname -m)." >&2
+        echo "Run ut-run-tests with --refresh-cache, or use a different cache volume." >&2
+        exit 1
+    fi
+}
+
+ensure_sublime_text_arch_matches
 sudo sh -e /etc/init.d/xvfb start
 ensure_git_identity
 ensure_ci_platform_compat
diff --git a/docker/ut-run-tests b/docker/ut-run-tests
old mode 100644
new mode 100755
index 6a857f7f..eb467e75
--- a/docker/ut-run-tests
+++ b/docker/ut-run-tests
@@ -2,4 +2,5 @@
 set -euo pipefail
 
 SCRIPT_DIR="$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd)"
-exec python "$SCRIPT_DIR/run_tests.py" "$@"
+PYTHON="$(command -v python3 || command -v python)"
+exec "$PYTHON" "$SCRIPT_DIR/run_tests.py" "$@"
diff --git a/sbin/install_sublime_text.sh b/sbin/install_sublime_text.sh
index 604786b1..5341a718 100644
--- a/sbin/install_sublime_text.sh
+++ b/sbin/install_sublime_text.sh
@@ -28,10 +28,13 @@ if [ -z $SUBLIME_TEXT_VERSION ]; then
 fi
 
 if [ -z $SUBLIME_TEXT_ARCH ]; then
-    SUBLIME_TEXT_ARCH=x64
+    case "$(uname -m)" in
+        aarch64|arm64) SUBLIME_TEXT_ARCH=arm64 ;;
+        *) SUBLIME_TEXT_ARCH=x64 ;;
+    esac
 fi
 
-if [ $SUBLIME_TEXT_VERSION -ge 4 ] && [ "$SUBLIME_TEXT_ARCH" != "x64" ]; then
+if [ $SUBLIME_TEXT_VERSION -ge 4 ] && [ "$SUBLIME_TEXT_ARCH" != "x64" ] && [ "$SUBLIME_TEXT_ARCH" != "arm64" ]; then
     echo "wrong value of $SUBLIME_TEXT_ARCH for Sublime Text version $SUBLIME_TEXT_VERSION"
     exit 1
 fi
@@ -132,7 +135,7 @@ else
         echo "installing sublime text $SUBLIME_TEXT_VERSION"
         for i in {1..20}; do
             if [ $SUBLIME_TEXT_VERSION -ge 4 ]; then
-                URL=$(curl -s "$STWEB" | sed -n 's/.*href="\([^"]*_x64\.tar\.xz\)".*/\1/p')
+                URL=$(curl -s "$STWEB" | sed -n "s/.*href=\"\([^\"]*_${SUBLIME_TEXT_ARCH}\.tar\.xz\)\".*/\1/p")
             else
                 if [ "$SUBLIME_TEXT_ARCH" = "x64" ]; then
                     URL=$(curl -s "$STWEB" | sed -n 's/.*href="\([^"]*x64\.tar\.bz2\)".*/\1/p')