diff --git a/setup.py b/setup.py
index 49db6f94..344805b5 100644
--- a/setup.py
+++ b/setup.py
@@ -25,6 +25,7 @@
     "google-api-core[grpc] >= 1.22.2, < 2.0.0dev",
     "grpc-google-iam-v1 >= 0.12.3, < 0.13dev",
     "proto-plus >= 1.4.0",
+    "packaging >= 14.3",
 ]
 
 extras = {"libcst": "libcst >= 0.2.5"}
diff --git a/testing/constraints-3.6.txt b/testing/constraints-3.6.txt
index 2686dc3f..3150727a 100644
--- a/testing/constraints-3.6.txt
+++ b/testing/constraints-3.6.txt
@@ -2,10 +2,11 @@
 # are correct in setup.py
 # List all library dependencies and extras in this file.
 # Pin the version to the lower bound.
-
 # e.g., if setup.py has "google-cloud-foo >= 1.14.0, < 2.0.0dev",
 # Then this file should have google-cloud-foo==1.14.0
 google-api-core==1.22.2
 proto-plus==1.4.0
 grpc-google-iam-v1==0.12.3
 libcst==0.2.5
+packaging==14.3
+google-auth==1.24.0  # TODO: remove when google-auth>=1.25.0 si transitively required through google-api-core