diff --git a/start.sh b/start.sh
index d6a65f9..675994f 100755
--- a/start.sh
+++ b/start.sh
@@ -11,15 +11,28 @@ function main {
   local help=false
   local sleep_seconds=$DEFAULT_SLEEP_SECONDS
   local config=""
+  local start_proxy=false
 
   local cmd=$0
 
-  # TODO --config is incompatible with --proxy, --bungee and standalone
   while [ $# -gt 0 ]; do
     local arg=$1
     case "$arg" in
       "--config" | "-c")
-        config=$2 #TODO ensure mode is valid
+        local mode=$2
+        case "$mode" in
+          "proxy" | "bungee" | "standalone")
+            ;;
+          case *)
+            err "Invalid mode for --config: $mode"
+            ;;
+        esac
+        config=$mode
+        if $proxy; then
+          err "--config can't be used together with --proxy"
+        elif $bungee; then
+          err "--config can't be used together with --bungee"
+        fi
         shift 2
         ;;
       "--sleep" | "-s")
@@ -30,6 +43,8 @@ function main {
         proxy=true
         if $bungee; then
           err "--proxy can't be used together with --bungee"
+        elif [[ -n $config ]]; then
+          err "--proxy can't be used together with --config"
         fi
         shift
         ;;
@@ -37,6 +52,8 @@ function main {
         bungee=true
         if $proxy; then
           err "--bungee can't be used together with --proxy"
+        elif [[ -n $config ]]; then
+          err "--bungee can't be used together with --config"
         fi
         shift
         ;;