diff --git a/setup.py b/setup.py
index b372a7f..5b313b7 100644
--- a/setup.py
+++ b/setup.py
@@ -33,6 +33,7 @@
 dependencies = [
     "google-api-core[grpc] >= 1.22.2, < 2.0.0dev",
     "proto-plus >= 1.10.0",
+    "packaging >= 14.3",
 ]
 extras = {}
 
diff --git a/testing/constraints-3.6.txt b/testing/constraints-3.6.txt
index 69e1c13..eb64cb3 100644
--- a/testing/constraints-3.6.txt
+++ b/testing/constraints-3.6.txt
@@ -7,3 +7,4 @@
 # Then this file should have foo==1.14.0
 google-api-core==1.22.2
 proto-plus==1.10.0
+packaging==14.3