diff --git a/google/auth/_default.py b/google/auth/_default.py
index 8e3b210..4dc0725 100644
--- a/google/auth/_default.py
+++ b/google/auth/_default.py
@@ -198,12 +198,25 @@
 def _get_explicit_environ_credentials():
     """Gets credentials from the GOOGLE_APPLICATION_CREDENTIALS environment
     variable."""
+    from google.auth import _cloud_sdk
+
+    cloud_sdk_adc_path = _cloud_sdk.get_application_default_credentials_path()
     explicit_file = os.environ.get(environment_vars.CREDENTIALS)
 
     _LOGGER.debug(
         "Checking %s for explicit credentials as part of auth process...", explicit_file
     )
 
+    if explicit_file is not None and explicit_file == cloud_sdk_adc_path:
+        # Cloud sdk flow calls gcloud to fetch project id, so if the explicit
+        # file path is cloud sdk credentials path, then we should fall back
+        # to cloud sdk flow, otherwise project id cannot be obtained.
+        _LOGGER.debug(
+            "Explicit credentials path %s is the same as Cloud SDK credentials path, fall back to Cloud SDK credentials flow...",
+            explicit_file,
+        )
+        return _get_gcloud_sdk_credentials()
+
     if explicit_file is not None:
         credentials, project_id = load_credentials_from_file(
             os.environ[environment_vars.CREDENTIALS]
diff --git a/google/auth/_default_async.py b/google/auth/_default_async.py
index 1a725af..d12a642 100644
--- a/google/auth/_default_async.py
+++ b/google/auth/_default_async.py
@@ -127,8 +127,17 @@
 def _get_explicit_environ_credentials():
     """Gets credentials from the GOOGLE_APPLICATION_CREDENTIALS environment
     variable."""
+    from google.auth import _cloud_sdk
+
+    cloud_sdk_adc_path = _cloud_sdk.get_application_default_credentials_path()
     explicit_file = os.environ.get(environment_vars.CREDENTIALS)
 
+    if explicit_file is not None and explicit_file == cloud_sdk_adc_path:
+        # Cloud sdk flow calls gcloud to fetch project id, so if the explicit
+        # file path is cloud sdk credentials path, then we should fall back
+        # to cloud sdk flow, otherwise project id cannot be obtained.
+        return _get_gcloud_sdk_credentials()
+
     if explicit_file is not None:
         credentials, project_id = load_credentials_from_file(
             os.environ[environment_vars.CREDENTIALS]