diff --git a/.github/workflows/tests.yaml b/.github/workflows/tests.yaml
index c09f0dbc..093fc338 100644
--- a/.github/workflows/tests.yaml
+++ b/.github/workflows/tests.yaml
@@ -33,6 +33,10 @@ jobs:
                     php-version: ${{ matrix.php }}
                     coverage: none
 
+            -   name: Require phpunit 5.7 for php >= 5.6
+                if: matrix.php >= 5.6
+                run: COMPOSER_MEMORY_LIMIT=-1 composer require "phpunit/phpunit:6.*" --no-interaction --no-update
+
             -   name: Require phpunit 6 for php >= 7.0
                 if: matrix.php >= 7.0
                 run: COMPOSER_MEMORY_LIMIT=-1 composer require "phpunit/phpunit:6.*" --no-interaction --no-update