diff --git a/.github/workflows/testing.yml b/.github/workflows/testing.yml
index e3fe4f7..270e6d9 100644
--- a/.github/workflows/testing.yml
+++ b/.github/workflows/testing.yml
@@ -72,7 +72,7 @@ jobs:
         with:
           php-version: ${{ matrix.php }}
           extensions: fileinfo, gd, imagick, exif, ffi
-          ini-values: zend.max_allowed_stack_size=-1
+          ini-values: zend.max_allowed_stack_size=-1, zend.assertions=1
 
       - name: Install libvips
         if: runner.os == 'Linux'