diff --git a/gcb/makestage/cloudbuild.yaml b/gcb/makestage/cloudbuild.yaml
index d6f4531..54c1f23 100644
--- a/gcb/makestage/cloudbuild.yaml
+++ b/gcb/makestage/cloudbuild.yaml
@@ -25,7 +25,7 @@ timeout: 2700s # 45m
 steps:
 # cert-manager relies on the git checkout to determine release version, among other things
 # By default, gcb only does a shallow clone, so we need to "unshallow" to get more details
-- name: gcr.io/cloud-builders/git
+- name: gcr.io/cloud-builders/git@sha256:1729e37322627125a813a1ec197e363a6745c149065bc223ba47353307fb5bbe
   dir: "go/src/github.com/cert-manager/cert-manager"
   entrypoint: bash
   args:
diff --git a/pkg/release/helm/testdata/cert-manager/values.yaml b/pkg/release/helm/testdata/cert-manager/values.yaml
index 49c8746..fc92098 100644
--- a/pkg/release/helm/testdata/cert-manager/values.yaml
+++ b/pkg/release/helm/testdata/cert-manager/values.yaml
@@ -8,7 +8,7 @@ image:
   repository: nginx
   pullPolicy: IfNotPresent
   # Overrides the image tag whose default is the chart appVersion.
-  tag: ""
+  tag: "@sha256:9dd288848f4495869f76676e419ae2d767ca99fece2ec37ec0261f9fdaab5204"
 
 imagePullSecrets: []
 nameOverride: ""