diff --git a/setup.py b/setup.py
index f5e45b3b..88175656 100644
--- a/setup.py
+++ b/setup.py
@@ -32,6 +32,7 @@
     "grpc-google-iam-v1 >= 0.12.3, < 0.13dev",
     "libcst >= 0.2.5",
     "proto-plus >= 1.4.0",
+    "packaging >= 14.3",
 ]
 
 package_root = os.path.abspath(os.path.dirname(__file__))
diff --git a/testing/constraints-3.6.txt b/testing/constraints-3.6.txt
index 770a9840..8dd34015 100644
--- a/testing/constraints-3.6.txt
+++ b/testing/constraints-3.6.txt
@@ -10,3 +10,5 @@ grpc-google-iam-v1==0.12.3
 libcst==0.2.5
 proto-plus==1.4.0
 google-auth==1.24.0 # TODO(busunkim): remove when google-auth>=1.25.0 is implicitly required through newer google-api-core
+packaging==14.3
+google-auth==1.24.0  # TODO: remove when google-auth>=1.25.0 si transitively required through google-api-core