diff --git a/install.sh b/install.sh
index e708726..e41b2fb 100755
--- a/install.sh
+++ b/install.sh
@@ -11,12 +11,18 @@ if [ "${EUID}" -ne 0 ]; then
   exit
 fi
 
-# check for existing Let's Encrypt install
-if [ -d "/etc/letsencrypt/" ]; then
-  echo "WARNING: Let's Encrypt is already installed."
-  echo "This installer will overwrite existing configurations."
-  echo -e "You have five seconds to execute ctrl-c to cancel this install.\a"
-  sleep 5
+# check for Ubuntu 22.04 (jammy) or Debian 12 (bookworm)
+os_codename=`lsb_release -cs`
+if [ $os_codename != jammy ] && [ $os_codename != bookworm ]; then
+  echo "This installer only runs on Ubuntu 22.04 (jammy) or Debian 12 (Bookworm), bailing out."
+  exit 1
+fi
+
+# check for existing web server software installs
+if [ -d "/etc/letsencrypt/" ] || [ -d "/opt/certbot/" ] || [ -f "/usr/bin/certbot" ]; then
+  echo "NOTICE: Let's Encrypt is already installed."
+  echo "You must purge any existing certbot installs before running this."
+  exit 1
 fi
 
 # Old apt installation instructions