diff --git a/setup.py b/setup.py
index f645527f..fb22b225 100644
--- a/setup.py
+++ b/setup.py
@@ -24,6 +24,7 @@
 dependencies = [
     "google-api-core[grpc] >= 1.22.2, < 2.0.0dev",
     "proto-plus >= 1.10.0",
+    "packaging >= 14.3",
 ]
 extras = {
     "libcst": "libcst >= 0.2.5",
diff --git a/testing/constraints-3.6.txt b/testing/constraints-3.6.txt
index 580415db..3833cd80 100644
--- a/testing/constraints-3.6.txt
+++ b/testing/constraints-3.6.txt
@@ -10,3 +10,5 @@ proto-plus==1.10.0
 libcst==0.2.5
 pandas==0.23.0
 google-cloud-storage==1.18.0
+packaging==14.3
+google-auth==1.24.0  # TODO: remove when google-auth>=1.25.0 si transitively required through google-api-core