diff --git a/gcb/makestage/cloudbuild.yaml b/gcb/makestage/cloudbuild.yaml
index d6f4531..c69b818 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:f83054a64625eef3404e02a29079a98e4b09d046a9fd1725eb89ce44784f0589
   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..a0ecfa2 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: "@sha256:341bf0f3ce6c5277d6002cf6e1fb0319fa4252add24ab6a0e262e0056d313208"
 
 imagePullSecrets: []
 nameOverride: ""