diff --git a/apex/amp/frontend.py b/apex/amp/frontend.py
index cbaf139dc..b97e5e796 100644
--- a/apex/amp/frontend.py
+++ b/apex/amp/frontend.py
@@ -1,4 +1,5 @@
 import torch
+import os
 from ._initialize import _initialize
 from ._amp_state import _amp_state, warn_or_err, maybe_print
 from collections import OrderedDict
@@ -422,6 +423,11 @@ def initialize(
     for k, v in _amp_state.opt_properties.options.items():
         maybe_print("{:26} : {}".format(k, v), True)
 
+
+    # Set flag to tell others apex.amp is enabled
+    os.environ["APEX_AMP_ENABLED"] = "1"
+
+
     return _initialize(models, optimizers, _amp_state.opt_properties, num_losses, cast_model_outputs)