diff --git a/google/auth/compute_engine/_metadata.py b/google/auth/compute_engine/_metadata.py
index 2861192..cba426f 100644
--- a/google/auth/compute_engine/_metadata.py
+++ b/google/auth/compute_engine/_metadata.py
@@ -32,9 +32,16 @@
 
 _LOGGER = logging.getLogger(__name__)
 
-_METADATA_ROOT = "http://{}/computeMetadata/v1/".format(
-    os.getenv(environment_vars.GCE_METADATA_ROOT, "metadata.google.internal")
-)
+# Environment variable GCE_METADATA_HOST is originally named
+# GCE_METADATA_ROOT. For compatiblity reasons, here it checks
+# the new variable first; if not set, the system falls back
+# to the old variable.
+_GCE_METADATA_HOST = os.getenv(environment_vars.GCE_METADATA_HOST, None)
+if not _GCE_METADATA_HOST:
+    _GCE_METADATA_HOST = os.getenv(
+        environment_vars.GCE_METADATA_ROOT, "metadata.google.internal"
+    )
+_METADATA_ROOT = "http://{}/computeMetadata/v1/".format(_GCE_METADATA_HOST)
 
 # This is used to ping the metadata server, it avoids the cost of a DNS
 # lookup.
diff --git a/google/auth/environment_vars.py b/google/auth/environment_vars.py
index 6a596f2..9c1367f 100644
--- a/google/auth/environment_vars.py
+++ b/google/auth/environment_vars.py
@@ -40,9 +40,15 @@
 
 # These two variables allow for customization of the addresses used when
 # contacting the GCE metadata service.
+GCE_METADATA_HOST = "GCE_METADATA_HOST"
 GCE_METADATA_ROOT = "GCE_METADATA_ROOT"
 """Environment variable providing an alternate hostname or host:port to be
-used for GCE metadata requests."""
+used for GCE metadata requests.
+
+This environment variable is originally named GCE_METADATA_ROOT. System will
+check the new variable first; should there be no value present,
+the system falls back to the old variable.
+"""
 
 GCE_METADATA_IP = "GCE_METADATA_IP"
 """Environment variable providing an alternate ip:port to be used for ip-only