diff --git a/Tests/AppVariableTest.php b/Tests/AppVariableTest.php
index ea3fbfda..9378e87c 100644
--- a/Tests/AppVariableTest.php
+++ b/Tests/AppVariableTest.php
@@ -43,7 +43,7 @@ public function testDebug($debugFlag)
         $this->assertEquals($debugFlag, $this->appVariable->getDebug());
     }
 
-    public static function debugDataProvider()
+    public static function debugDataProvider(): array
     {
         return [
             'debug on' => [true],
diff --git a/Tests/Command/LintCommandTest.php b/Tests/Command/LintCommandTest.php
index a898680f..18d09b20 100644
--- a/Tests/Command/LintCommandTest.php
+++ b/Tests/Command/LintCommandTest.php
@@ -150,7 +150,7 @@ public function testComplete(array $input, array $expectedSuggestions)
         $this->assertSame($expectedSuggestions, $tester->complete($input));
     }
 
-    public static function provideCompletionSuggestions()
+    public static function provideCompletionSuggestions(): iterable
     {
         yield 'option' => [['--format', ''], ['txt', 'json', 'github']];
     }
diff --git a/Tests/Extension/FormExtensionDivLayoutTest.php b/Tests/Extension/FormExtensionDivLayoutTest.php
index 3809f3fa..5de8fb90 100644
--- a/Tests/Extension/FormExtensionDivLayoutTest.php
+++ b/Tests/Extension/FormExtensionDivLayoutTest.php
@@ -100,7 +100,7 @@ public function testThemeBlockInheritanceUsingDynamicExtend()
         );
     }
 
-    public static function isSelectedChoiceProvider()
+    public static function isSelectedChoiceProvider(): array
     {
         return [
             [true, '0', '0'],
@@ -150,7 +150,7 @@ public function testStartTagHasActionAttributeWhenActionIsZero()
         $this->assertSame('<form name="form" method="get" action="0">', $html);
     }
 
-    public static function isRootFormProvider()
+    public static function isRootFormProvider(): array
     {
         return [
             [true, new FormView()],
@@ -381,14 +381,14 @@ protected function setTheme(FormView $view, array $themes, $useDefaultThemes = t
         $this->renderer->setTheme($view, $themes, $useDefaultThemes);
     }
 
-    public static function themeBlockInheritanceProvider()
+    public static function themeBlockInheritanceProvider(): array
     {
         return [
             [['theme.html.twig']],
         ];
     }
 
-    public static function themeInheritanceProvider()
+    public static function themeInheritanceProvider(): array
     {
         return [
             [['parent_label.html.twig'], ['child_label.html.twig']],