diff --git a/shim/PACKAGE b/shim/PACKAGE
index ea35fecd..782e6f91 100644
--- a/shim/PACKAGE
+++ b/shim/PACKAGE
@@ -5,8 +5,11 @@
 # License, Version 2.0 found in the LICENSE-APACHE file in the root directory
 # of this source tree.
 
-load(":cfg.bzl", "get_shim_modifiers")
+load(":cfg.bzl", "SHIM_ALIASES", "set_cfg_constructor", "get_shim_modifiers")
 load("@prelude//cfg/modifier:set_cfg_modifiers.bzl", "set_cfg_modifiers")
 
+# Activate cfg modifiers from CLI / PACKAGE / targets
+set_cfg_constructor(SHIM_ALIASES)
+
 modifiers = get_shim_modifiers()
 set_cfg_modifiers(modifiers)
diff --git a/shim/cfg.bzl b/shim/cfg.bzl
index 9c630dfa..9b63ae11 100644
--- a/shim/cfg.bzl
+++ b/shim/cfg.bzl
@@ -13,10 +13,10 @@ SHIM_ALIASES = {
     "ubuntu": "shim//os/linux/distro/constraints:ubuntu",
 }
 
-CFG_CONSTRUCTOR_INITIALIZED_KEY = "buck.cfg_constructor_initialized"
-
 def set_cfg_constructor(aliases = dict()):
-    if not read_parent_package_value(CFG_CONSTRUCTOR_INITIALIZED_KEY):
+    project_root_cell = read_root_config("cell_aliases", "root")
+    current_root_cell = read_config("cell_aliases", "root")
+    if project_root_cell == current_root_cell:
         native.set_cfg_constructor(
             stage0 = cfg_constructor_pre_constraint_analysis,
             stage1 = cfg_constructor_post_constraint_analysis,
@@ -25,8 +25,6 @@ def set_cfg_constructor(aliases = dict()):
             extra_data = struct(),
         )
 
-        write_package_value(CFG_CONSTRUCTOR_INITIALIZED_KEY, True)
-
 def get_shim_modifiers():
     modifiers = []