diff --git a/tests/element_helper_test.php b/tests/element_helper_test.php
index f44f3dd..df8a12a 100644
--- a/tests/element_helper_test.php
+++ b/tests/element_helper_test.php
@@ -40,7 +40,7 @@ class mod_customcert_element_helper_testcase extends advanced_testcase {
     /**
      * Test set up.
      */
-    public function setUp() {
+    public function setUp(): void {
         $this->resetAfterTest();
     }
 
diff --git a/tests/email_certificate_task_test.php b/tests/email_certificate_task_test.php
index 285acd6..f4d490a 100644
--- a/tests/email_certificate_task_test.php
+++ b/tests/email_certificate_task_test.php
@@ -38,7 +38,7 @@ class mod_customcert_task_email_certificate_task_testcase extends advanced_testc
     /**
      * Test set up.
      */
-    public function setUp() {
+    public function setUp(): void {
         $this->resetAfterTest();
     }
 
diff --git a/tests/external_test.php b/tests/external_test.php
index 6540e64..c46f303 100644
--- a/tests/external_test.php
+++ b/tests/external_test.php
@@ -40,7 +40,7 @@ class mod_customcert_external_test_testcase extends advanced_testcase {
     /**
      * Test set up.
      */
-    public function setUp() {
+    public function setUp(): void {
         $this->resetAfterTest();
     }