diff --git a/cmd/rollcall/deploy.go b/cmd/rollcall/deploy.go
index 2e098c9..4dfdf4e 100644
--- a/cmd/rollcall/deploy.go
+++ b/cmd/rollcall/deploy.go
@@ -297,7 +297,11 @@ func (a *App) renderSeed(j *Job, sp DeploySpec, token string) []seedFile {
 		if len(sp.Packages) > 0 {
 			fmt.Fprintf(&b, "packages: %s\n", yamlList(sp.Packages))
 		}
-		fmt.Fprintf(&b, "phone_home:\n  url: %s/api/v1/phone-home/%s\n  post: [instance_id, hostname, fqdn, pub_key_ed25519]\n  tries: 10\n", base, token)
+		home := base
+		if t := a.agentTLS(base); t != "" && a.ca != nil {
+			home = t // the deployed OS trusts the Rollcall CA (bootcmd below), so it calls home over HTTPS
+		}
+		fmt.Fprintf(&b, "phone_home:\n  url: %s/api/v1/phone-home/%s\n  post: [instance_id, hostname, fqdn, pub_key_ed25519]\n  tries: 10\n", home, token)
 		b.WriteString("final_message: \"rollcall: deployed, up after $UPTIME s\"\n") // only $UPTIME/$TIMESTAMP/$DATASOURCE/$VERSION are expanded
 		ud = b.String()
 	}
diff --git a/images/compute-debian13/includes/usr/local/sbin/rollcall-overlay b/images/compute-debian13/includes/usr/local/sbin/rollcall-overlay
index fba4d9e..8e6e703 100755
--- a/images/compute-debian13/includes/usr/local/sbin/rollcall-overlay
+++ b/images/compute-debian13/includes/usr/local/sbin/rollcall-overlay
@@ -3,13 +3,18 @@
 # Fetches this node's overlay tarball from the rollcall server (identified by
 # the rollcall.node token on the kernel command line), applies it over / when
 # it changed, then runs /run/rollcall/post-<stage>.sh if the overlay shipped one.
+# With rollcall.tls= and rollcall.ca= on the command line it talks HTTPS: the
+# CA certificate is accepted only by that SHA-256, and there is no fallback
+# to HTTP (the overlay carries secrets such as munge.key).
 set -eu
 stage=${1:-system}
-SERVER=""; TOKEN=""
+SERVER=""; TOKEN=""; TLS=""; CA=""
 for t in $(cat /proc/cmdline); do
   case $t in
     rollcall.server=*) SERVER=${t#*=} ;;
     rollcall.node=*)   TOKEN=${t#*=} ;;
+    rollcall.tls=*)    TLS=${t#*=} ;;
+    rollcall.ca=*)     CA=$(echo "${t#*=}" | tr -d ':' | tr 'A-F' 'a-f') ;;
   esac
 done
 if [ -z "$SERVER" ] || [ -z "$TOKEN" ]; then
@@ -17,9 +22,30 @@ if [ -z "$SERVER" ] || [ -z "$TOKEN" ]; then
   exit 0
 fi
 mkdir -p /run/rollcall
+CURL_CA=""
+if [ -n "$TLS" ] && [ -n "$CA" ]; then
+  cafile=/run/rollcall/ca.pem
+  if [ ! -s "$cafile" ]; then
+    i=0
+    until curl -fsS --connect-timeout 5 "$SERVER/ca.pem" -o "$cafile.new"; do
+      i=$((i+1)); [ "$i" -ge 30 ] && { echo "rollcall-overlay: cannot fetch the CA certificate" >&2; exit 1; }
+      sleep 5
+    done
+    got=$(openssl x509 -in "$cafile.new" -outform DER | sha256sum | cut -d' ' -f1)
+    if [ "$got" != "$CA" ]; then
+      rm -f "$cafile.new"
+      echo "rollcall-overlay: the CA certificate does not match rollcall.ca; not fetching the overlay" >&2
+      exit 1
+    fi
+    mv -f "$cafile.new" "$cafile"
+  fi
+  SERVER=$TLS
+  CURL_CA="--cacert $cafile"
+fi
 tmp=/run/rollcall/$stage.tar.new
 i=0
-until curl -fsS --connect-timeout 5 -H "X-Rollcall-Node: $TOKEN" \
+# shellcheck disable=SC2086 # CURL_CA is two words or none
+until curl -fsS --connect-timeout 5 $CURL_CA -H "X-Rollcall-Node: $TOKEN" \
       "$SERVER/api/v1/nodes/self/overlay?stage=$stage" -o "$tmp"; do
   i=$((i+1))
   if [ "$i" -ge 60 ]; then echo "rollcall-overlay: server unreachable" >&2; exit 1; fi