diff --git a/azure-pipelines/templates/ci-git-rebase.yml b/azure-pipelines/templates/ci-git-rebase.yml
--- a/azure-pipelines/templates/ci-git-rebase.yml
+++ b/azure-pipelines/templates/ci-git-rebase.yml
@@ -6,5 +6,5 @@ steps:
     git config user.email 'info@openttd.org'
     git config user.name 'OpenTTD CI'
     git rebase origin/${SYSTEM_PULLREQUEST_TARGETBRANCH}
-  displayName: 'Rebase to $(System.PullRequest.TargetBranch)'
+  displayName: 'Rebase to target branch'
   condition: and(succeeded(), eq(variables['Build.Reason'], 'PullRequest'))
diff --git a/azure-pipelines/templates/linux-build.yml b/azure-pipelines/templates/linux-build.yml
--- a/azure-pipelines/templates/linux-build.yml
+++ b/azure-pipelines/templates/linux-build.yml
@@ -4,11 +4,27 @@ parameters:
   ContainerCommand: ''
 
 steps:
+# 'envVars' in the 'Docker@1' task is a bit funky. When you want to use a
+# variable, you have to quote it. But the quote is also sent directly to
+# Docker and ends up in the variable, which you don't want. To work around
+# this, we set the correct variable first (which becomes an env-variable), and
+# pass that env-variable through to Docker. We cannot use the normal
+# 'variables' entry, as we are a template. So that results in this bit of
+# Bash code. Not because it is pretty, but it is the only way we found that
+# works.
+- bash: |
+    echo "##vso[task.setvariable variable=TARGET_BRANCH]${SYSTEM_PULLREQUEST_TARGETBRANCH}"
+    echo "Target branch is ${SYSTEM_PULLREQUEST_TARGETBRANCH}"
+  displayName: "Set target branch"
+  condition: and(succeeded(), eq(variables['Build.Reason'], 'PullRequest'))
+
 - task: Docker@1
   ${{ if eq(parameters.Image, 'compile-farm') }}:
     displayName: 'Build'
   ${{ if eq(parameters.Image, 'compile-farm-ci') }}:
     displayName: 'Build and test'
+  ${{ if eq(parameters.Tag, 'commit-checker') }}:
+    condition: and(succeeded(), eq(variables['Build.Reason'], 'PullRequest'))
   inputs:
     command: 'Run an image'
     imageName: openttd/${{ parameters.Image }}:${{ parameters.Tag }}
@@ -16,3 +32,5 @@ steps:
     workingDirectory: '$(Build.SourcesDirectory)'
     containerCommand: ${{ parameters.ContainerCommand }}
     runInBackground: false
+    envVars: |
+      TARGET_BRANCH