diff --git a/setup.py b/setup.py
index 16489eb..7831995 100644
--- a/setup.py
+++ b/setup.py
@@ -28,6 +28,7 @@
     "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",
     "grafeas >=1.0.0, <2.0dev",
 ]
 extras = {"libcst": "libcst >= 0.2.5"}
diff --git a/testing/constraints-3.6.txt b/testing/constraints-3.6.txt
index 0b693e2..e0d47f7 100644
--- a/testing/constraints-3.6.txt
+++ b/testing/constraints-3.6.txt
@@ -10,3 +10,5 @@ grpc-google-iam-v1==0.12.3
 proto-plus==1.4.0
 libcst==0.2.5
 grafeas==1.0.0
+packaging==14.3
+google-auth==1.24.0  # TODO: remove when google-auth>=1.25.0 is transitively required through google-api-core