diff --git a/htdocs/account/index.php b/htdocs/account/index.php
index 6d4aa284487407a04a1afdd0cf8a2a38410a0582..725133e326b9a111c34b3ff9f3971c3fbf495148 100644
--- a/htdocs/account/index.php
+++ b/htdocs/account/index.php
@@ -155,7 +155,7 @@ function accountprefs_validate(Pieform $form, $values) {
         if (!AuthInternal::is_username_valid($values['username'])) {
             $form->set_error('username', get_string('usernameinvalidform', 'auth.internal'));
         }
-        if (!$form->get_error('username') && record_exists_select('usr', 'LOWER(username) = ?', strtolower($values['username']))) {
+        if (!$form->get_error('username') && record_exists_select('usr', 'LOWER(username) = ?', array(strtolower($values['username'])))) {
             $form->set_error('username', get_string('usernamealreadytaken', 'auth.internal'));
         }
     }
diff --git a/htdocs/admin/users/add.php b/htdocs/admin/users/add.php
index b2e93da9b14b562477602aca3f48b3549778b7f8..87aa8bbc3434377bae1468700a96bf039429943a 100644
--- a/htdocs/admin/users/add.php
+++ b/htdocs/admin/users/add.php
@@ -194,7 +194,7 @@ function adduser_validate(Pieform $form, $values) {
             $form->set_error('username', get_string('usernameinvalidform', 'auth.internal'));
         }
     }
-    if (!$form->get_error('username') && record_exists_select('usr', 'LOWER(username) = ?', strtolower($username))) {
+    if (!$form->get_error('username') && record_exists_select('usr', 'LOWER(username) = ?', array(strtolower($username)))) {
         $form->set_error('username', get_string('usernamealreadytaken', 'auth.internal'));
     }
 
diff --git a/htdocs/admin/users/edit.php b/htdocs/admin/users/edit.php
index b0ecaec92f667240db26a52726eb8fc9223afc47..6af5c74a918c85e0a0d90ef8bba29e007d339860 100644
--- a/htdocs/admin/users/edit.php
+++ b/htdocs/admin/users/edit.php
@@ -287,7 +287,7 @@ function edituser_site_validate(Pieform $form, $values) {
                 }
             }
 
-            if (!$form->get_error('username') && record_exists_select('usr', 'LOWER(username) = ?', strtolower($values['username']))) {
+            if (!$form->get_error('username') && record_exists_select('usr', 'LOWER(username) = ?', array(strtolower($values['username'])))) {
                 $form->set_error('username', get_string('usernamealreadytaken', 'auth.internal'));
             }
         }
diff --git a/htdocs/admin/users/uploadcsv.php b/htdocs/admin/users/uploadcsv.php
index d449efe55e4e5cb212de2207f8b9578fbef3ea25..68c4979320297ca2a1c1d4e2dd5e7e30ba450c9b 100644
--- a/htdocs/admin/users/uploadcsv.php
+++ b/htdocs/admin/users/uploadcsv.php
@@ -309,7 +309,7 @@ function uploadcsv_validate(Pieform $form, $values) {
             $csverrors->add($i, get_string('uploadcsverroruseralreadyexists', 'admin', $i, $username));
         }
         else {
-            if (!$values['updateusers'] && record_exists_select('usr', 'LOWER(username) = ?', strtolower($username))) {
+            if (!$values['updateusers'] && record_exists_select('usr', 'LOWER(username) = ?', array(strtolower($username)))) {
                 $csverrors->add($i, get_string('uploadcsverroruseralreadyexists', 'admin', $i, $username));
             }
             $usernames[strtolower($username)] = array(
diff --git a/htdocs/auth/lib.php b/htdocs/auth/lib.php
index bb67622a96b7915f49f19eee000ff3c105e68f33..ebb6d42fee8f53afd3f240a9f8931c47688c23f1 100644
--- a/htdocs/auth/lib.php
+++ b/htdocs/auth/lib.php
@@ -975,7 +975,7 @@ function requiredfields_validate(Pieform $form, $values) {
             if (!AuthInternal::is_username_valid($values['username'])) {
                 $form->set_error('username', get_string('usernameinvalidform', 'auth.internal'));
             }
-            if (!$form->get_error('username') && record_exists_select('usr', 'LOWER(username) = ?', strtolower($values['username']))) {
+            if (!$form->get_error('username') && record_exists_select('usr', 'LOWER(username) = ?', array(strtolower($values['username'])))) {
                 $form->set_error('username', get_string('usernamealreadytaken', 'auth.internal'));
             }
         }