diff --git a/setup.py b/setup.py
index f3ad80b8..a4ee54a8 100644
--- a/setup.py
+++ b/setup.py
@@ -26,6 +26,7 @@
 dependencies = [
     "google-api-core[grpc] >= 1.22.2, < 2.0.0dev",
     "proto-plus >= 0.4.0",
+    "packaging >= 14.3",
 ]
 
 extras = {"libcst": "libcst >= 0.2.5"}
diff --git a/testing/constraints-3.6.txt b/testing/constraints-3.6.txt
index 2a5b1cbf..f88167ff 100644
--- a/testing/constraints-3.6.txt
+++ b/testing/constraints-3.6.txt
@@ -8,3 +8,5 @@
 google-api-core==1.22.2
 proto-plus==0.4.0
 libcst==0.2.5
+packaging==14.3
+google-auth==1.24.0  # TODO: remove when google-auth>=1.25.0 is required through google-api-core