diff --git a/lang/en/error.php b/lang/en/error.php
index 1acf56bc9a91f..8588576e4fd65 100644
--- a/lang/en/error.php
+++ b/lang/en/error.php
@@ -144,6 +144,7 @@
 $string['cannotsetupcapformod'] = 'Could not set up the capabilities for {$a}';
 $string['cannotsetupcapforplugin'] = 'Could not set up the capabilities for {$a}';
 $string['cannotshowhidecoursesincategory'] = 'Cannot show/hide the courses in category {$a}.';
+$string['cannotsignup'] = 'You cannot create a new account because you are already logged in as {$a}.';
 $string['cannotunassigncap'] = 'Could not unassign deprecated capability {$a->cap} from role {$a->role}';
 $string['cannotunassignrolefrom'] = 'Cannot unassign this user from role id: {$a}';
 $string['cannotunzipfile'] = 'Cannot unzip file';
diff --git a/login/signup.php b/login/signup.php
index 976b3420f8784..66e622c1bf4a9 100644
--- a/login/signup.php
+++ b/login/signup.php
@@ -48,6 +48,22 @@
 $PAGE->set_url('/login/signup.php');
 $PAGE->set_context(context_system::instance());
 
+// Override wanted URL, we do not want to end up here again if user clicks "Login".
+$SESSION->wantsurl = $CFG->wwwroot . '/';
+
+if (isloggedin() and !isguestuser()) {
+    // Prevent signing up when already logged in.
+    echo $OUTPUT->header();
+    echo $OUTPUT->box_start();
+    $logout = new single_button(new moodle_url($CFG->httpswwwroot . '/login/logout.php',
+        array('sesskey' => sesskey(), 'loginpage' => 1)), get_string('logout'), 'post');
+    $continue = new single_button(new moodle_url('/'), get_string('cancel'), 'get');
+    echo $OUTPUT->confirm(get_string('cannotsignup', 'error', fullname($USER)), $logout, $continue);
+    echo $OUTPUT->box_end();
+    echo $OUTPUT->footer();
+    exit;
+}
+
 $mform_signup = $authplugin->signup_form();
 
 if ($mform_signup->is_cancelled()) {