diff --git a/deploy/unifi.sh b/deploy/unifi.sh
index a864135e..68bce9d6 100644
--- a/deploy/unifi.sh
+++ b/deploy/unifi.sh
@@ -5,6 +5,18 @@
 #   - self-hosted Unifi Controller
 #   - Unifi Cloud Key (Gen1/2/2+)
 #   - Unifi Cloud Key running UnifiOS (v2.0.0+, Gen2/2+ only)
+#     See below regarding keytool. Not tested.
+#   - Unifi Dream Machine
+#       This has not been tested on other "all-in-one" devices such as
+#       UDM Pro or Unifi Express.
+#
+#       OS Version v2.0.0+
+#       Network Application version 7.0.0+
+#       OS version ~3.1 removed java and keytool from the UnifiOS. These must be
+#         manually installed by the system owner at their own risk, as 
+#         doing so may invalidate official Ubiquiti support/warranty.
+#         `apt update && apt install openjdk-11-jre-headless -y`
+# 
 # Please report bugs to https://github.com/acmesh-official/acme.sh/issues/3359
 
 #returns 0 means success, otherwise error.
@@ -74,14 +86,30 @@ unifi_deploy() {
   _reload_cmd=""
 
   # Unifi Controller environment (self hosted or any Cloud Key) --
-  # auto-detect by file /usr/lib/unifi/data/keystore:
+  # auto-detect by file /usr/lib/unifi/data/keystore
+  # Additional detection of OS version to handle missing keytool.
   _unifi_keystore="${DEPLOY_UNIFI_KEYSTORE:-/usr/lib/unifi/data/keystore}"
   if [ -f "$_unifi_keystore" ]; then
-    _info "Installing certificate for Unifi Controller (Java keystore)"
     _debug _unifi_keystore "$_unifi_keystore"
     if ! _exists keytool; then
-      _err "keytool not found"
+      _err "keytool not found."
+      _keytool_instructions=$(cat <<-EOF
+      Unifi removed keytool from the console OS after version 3. 
+      You may be able to reinstall with
+      "apt update && apt install openjdk-11-jre-headless -y"
+      THIS MAY AFFECT UBIQUITI SUPPORT, DO SO AT YOUR OWN RISK.
+      It's also possible that apt will not work in future versions.
+      
+      If you don't want to (or can't use apt), then it's recommended
+      to deploy from a remote host via SSH. See
+      https://github.com/acmesh-official/acme.sh/wiki/deployhooks#examples-using-ssh-deploy
+
+EOF
+)
+      _info "$_keytool_instructions"
       return 1
+    else
+      _info "Installing certificate for Unifi Controller (Java keystore)"
     fi
     if [ ! -w "$_unifi_keystore" ]; then
       _err "The file $_unifi_keystore is not writable, please change the permission."
@@ -99,13 +127,23 @@ unifi_deploy() {
       return 1
     fi
 
+    # Save the existing keystore in case something goes wrong.
+    cp -f "${_unifi_keystore}" "${_unifi_keystore}"_original
+    _info "Previous certificate and key saved to ${_unifi_keystore}_original."
+
+    # May not be necessary, but seems more reliable
+    _debug "Remove existing key from keystore: $_unifi_keystore"
+    if keytool -delete -alias unifi -keystore "$_unifi_keystore" \
+      -deststorepass "$_unifi_keypass"; then
+      _debug "Successfully removed old certificate from keystore."
+    fi
+
     _debug "Import into keystore: $_unifi_keystore"
     if keytool -importkeystore \
       -deststorepass "$_unifi_keypass" -destkeypass "$_unifi_keypass" -destkeystore "$_unifi_keystore" \
       -srckeystore "$_import_pkcs12" -srcstoretype PKCS12 -srcstorepass "$_unifi_keypass" \
       -alias unifi -noprompt; then
       _debug "Import keystore success!"
-      rm "$_import_pkcs12"
     else
       _err "Error importing into Unifi Java keystore."
       _err "Please re-run with --debug and report a bug."
@@ -113,6 +151,24 @@ unifi_deploy() {
       return 1
     fi
 
+    # Update unifi service for certificate cipher compatibility
+    if ${ACME_OPENSSL_BIN:-openssl} pkcs12 \
+      -in "$_import_pkcs12" \
+      -password pass:aircontrolenterprise \
+      -nokeys | ${ACME_OPENSSL_BIN:-openssl} x509 -text \
+      -noout | grep -i "signature" | grep -iq ecdsa > /dev/null 2>&1; then
+      cp -f /usr/lib/unifi/data/system.properties /usr/lib/unifi/data/system.properties_original
+      _info "Updating system configuration for cipher compatibility."
+      _info "Saved original system config to /usr/lib/unifi/data/system.properties_original"
+      sed -i '/unifi\.https\.ciphers/d' /usr/lib/unifi/data/system.properties
+      echo "unifi.https.ciphers=ECDHE-ECDSA-AES256-GCM-SHA384,ECDHE-RSA-AES128-GCM-SHA256" &>> /usr/lib/unifi/data/system.properties
+      sed -i '/unifi\.https\.sslEnabledProtocols/d' /usr/lib/unifi/data/system.properties
+      echo "unifi.https.sslEnabledProtocols=TLSv1.3,TLSv1.2" &>> /usr/lib/unifi/data/system.properties
+      _info "System configuration updated."
+    fi
+
+    rm "$_import_pkcs12"
+
     if systemctl -q is-active unifi; then
       _reload_cmd="${_reload_cmd:+$_reload_cmd && }service unifi restart"
     fi
@@ -165,6 +221,11 @@ unifi_deploy() {
       return 1
     fi
 
+    # Save the existing certs in case something goes wrong.
+    cp -f "${_unifi_core_config}"/unifi-core.crt "${_unifi_core_config}"/unifi-core_original.crt
+    cp -f "${_unifi_core_config}"/unifi-core.key "${_unifi_core_config}"/unifi-core_original.key
+    _info "Previous certificate and key saved to ${_unifi_core_config}/unifi-core_original.crt/key."
+
     cat "$_cfullchain" >"${_unifi_core_config}/unifi-core.crt"
     cat "$_ckey" >"${_unifi_core_config}/unifi-core.key"