diff --git a/bin/acme b/bin/acme
index 3424a11..7e21837 100755
--- a/bin/acme
+++ b/bin/acme
@@ -125,7 +125,13 @@ Amp\run(function () use ($command, $climate) {
     };
 
     try {
-        yield $command->execute($climate->arguments);
+        $exitCode = (yield $command->execute($climate->arguments));
+
+        if ($exitCode === null) {
+            $logger->warning("Invalid exit code: null, falling back to 0. Please consider reporting this as bug.");
+        }
+
+        exit($exitCode);
     } catch (Throwable $e) {
         $handler($e);
     } catch (Exception $e) {
diff --git a/src/Commands/Setup.php b/src/Commands/Setup.php
index 40df5ec..da55ff7 100644
--- a/src/Commands/Setup.php
+++ b/src/Commands/Setup.php
@@ -57,6 +57,8 @@ class Setup implements Command {
         /** @var Registration $registration */
         $registration = (yield $acme->register($email));
         $this->climate->whisper("Registration successful with the following contact information: " . implode(", ", $registration->getContact()));
+
+        return 0;
     }
 
     private function checkEmail($email) {