diff --git a/core/dbt/contracts/project.py b/core/dbt/contracts/project.py
index d931c3371cb..c2090eb4d10 100644
--- a/core/dbt/contracts/project.py
+++ b/core/dbt/contracts/project.py
@@ -331,7 +331,7 @@ class ProjectFlags(ExtensibleDbtClassMixin):
     write_json: Optional[bool] = None
 
     # legacy behaviors
-    require_explicit_package_overrides_for_builtin_materializations: bool = False
+    require_explicit_package_overrides_for_builtin_materializations: bool = True
     require_resource_names_without_spaces: bool = False
     source_freshness_run_project_hooks: bool = False
 
diff --git a/tests/functional/materializations/test_custom_materialization.py b/tests/functional/materializations/test_custom_materialization.py
index 2c3ec4e74c2..0a100021db2 100644
--- a/tests/functional/materializations/test_custom_materialization.py
+++ b/tests/functional/materializations/test_custom_materialization.py
@@ -37,11 +37,8 @@ def packages(self):
 
     def test_adapter_dependency(self, project, override_view_adapter_dep, set_up_deprecations):
         run_dbt(["deps"])
-        # this should error because the override is buggy
-        run_dbt(["run"], expect_pass=False)
-
-        # overriding a built-in materialization scoped to adapter from package is deprecated
-        assert deprecations.active_deprecations == {"package-materialization-override"}
+        # this should pass because implicit overrides are now deprecated (= disabled by default)
+        run_dbt(["run"])
 
 
 class TestOverrideAdapterDependencyDeprecated:
@@ -101,11 +98,8 @@ def packages(self):
 
     def test_default_dependency(self, project, override_view_default_dep, set_up_deprecations):
         run_dbt(["deps"])
-        # this should error because the override is buggy
-        run_dbt(["run"], expect_pass=False)
-
-        # overriding a built-in materialization from package is deprecated
-        assert deprecations.active_deprecations == {"package-materialization-override"}
+        # this should pass because implicit overrides are now deprecated (= disabled by default)
+        run_dbt(["run"])
 
 
 class TestOverrideDefaultDependencyDeprecated: