diff --git a/.kokoro/gas/trigger-protobuf.cfg b/.kokoro/gas/trigger-protobuf.cfg
index e46d128..256e10c 100644
--- a/.kokoro/gas/trigger-protobuf.cfg
+++ b/.kokoro/gas/trigger-protobuf.cfg
@@ -31,7 +31,7 @@ env_vars: {
 # List of minor Ruby versions for protobuf builds, colon-delimited.
 env_vars: {
   key: "GAS_RUBY_VERSIONS"
-  value: "3.1:3.2:3.3:3.4"
+  value: "3.1:3.2:3.3:3.4:4.0"
 }
 
 # Path to the RubyGems API key file for the protobuf account.