diff --git a/spanner/setup.py b/spanner/setup.py
index 7498d54abfd6..1ece643bd6fe 100644
--- a/spanner/setup.py
+++ b/spanner/setup.py
@@ -52,6 +52,7 @@
 
 REQUIREMENTS = [
     'google-cloud-core >= 0.27.0, < 0.28dev',
+    'google-auth >= 1.1.0',
     'grpcio >= 1.2.0, < 2.0dev',
     'gapic-google-cloud-spanner-v1 >= 0.15.0, < 0.16dev',
     'gapic-google-cloud-spanner-admin-database-v1 >= 0.15.0, < 0.16dev',