diff --git a/src/tests/cogl/conform/meson.build b/src/tests/cogl/conform/meson.build
index b43976fae..02e5481c7 100644
--- a/src/tests/cogl/conform/meson.build
+++ b/src/tests/cogl/conform/meson.build
@@ -88,6 +88,7 @@ foreach cogl_test: cogl_tests
   foreach variant: cogl_test_variants
     variant_test_env = test_env
     variant_test_env.set('COGL_DRIVER', variant)
+    variant_test_env.set('COGL_DEBUG', 'winsys')
 
     test(test_name + '-' + variant, test_executable,
       suite: ['cogl', 'cogl/conform'],
diff --git a/src/tests/cogl/unit/meson.build b/src/tests/cogl/unit/meson.build
index f46a3df42..937335d90 100644
--- a/src/tests/cogl/unit/meson.build
+++ b/src/tests/cogl/unit/meson.build
@@ -44,6 +44,7 @@ foreach unit_test: cogl_unit_tests
       variant_test_env = test_env
       variant_test_env.set('COGL_DRIVER', variant)
     endif
+    variant_test_env.set('COGL_DEBUG', 'winsys')
 
     test('@0@-@1@'.format(test_name, variant), test_executable,
       suite: ['cogl', 'cogl/unit'],