diff --git a/google/api_core/operations_v1/abstract_operations_client.py b/google/api_core/operations_v1/abstract_operations_client.py
index 714c2aae..38f532af 100644
--- a/google/api_core/operations_v1/abstract_operations_client.py
+++ b/google/api_core/operations_v1/abstract_operations_client.py
@@ -14,7 +14,6 @@
 # limitations under the License.
 #
 from collections import OrderedDict
-from distutils import util
 import os
 import re
 from typing import Dict, Optional, Sequence, Tuple, Type, Union
@@ -294,13 +293,16 @@ def __init__(
             client_options = client_options_lib.ClientOptions()
 
         # Create SSL credentials for mutual TLS if needed.
-        use_client_cert = bool(
-            util.strtobool(os.getenv("GOOGLE_API_USE_CLIENT_CERTIFICATE", "false"))
-        )
-
+        use_client_cert = os.getenv(
+            "GOOGLE_API_USE_CLIENT_CERTIFICATE", "false"
+        ).lower()
+        if use_client_cert not in ("true", "false"):
+            raise ValueError(
+                "Environment variable `GOOGLE_API_USE_CLIENT_CERTIFICATE` must be either `true` or `false`"
+            )
         client_cert_source_func = None
         is_mtls = False
-        if use_client_cert:
+        if use_client_cert == "true":
             if client_options.client_cert_source:
                 is_mtls = True
                 client_cert_source_func = client_options.client_cert_source