diff --git a/internal/runner/runner.go b/internal/runner/runner.go
index b4b7846..98461f6 100644
--- a/internal/runner/runner.go
+++ b/internal/runner/runner.go
@@ -25,20 +25,6 @@ func NewRunner(driver ContainerDriver, labels map[string]string) Runner {
 	}
 }
 
-func (r *Runner) GetImageUriByLabel(label string) string {
-	uri, exists := r.Labels[label]
-
-	if exists {
-		return uri
-	}
-
-	return "debian:latest"
-}
-
-func (r *Runner) GetContainerName(jobId string) string {
-	return fmt.Sprintf("runner-%s", jobId)
-}
-
 // Executes a workflow using the runner.
 //
 // This is the high-level call that will set up the container
@@ -62,8 +48,14 @@ func (r *Runner) RunWorkflow(workflow workflow.Workflow) TaskTracker {
 				defer groupWait.Done()
 				jobTracker := NewTaskTracker(rootTracker).SetStatus("started")
 
-				runnerImage := r.GetImageUriByLabel(job.RunsOn)
-				containerName := r.GetContainerName(jobTracker.TaskId)
+				runnerImage, defined := r.Labels[job.RunsOn]
+
+				if !defined {
+					jobTracker.SetStatus("failed").SetError(fmt.Errorf("Unknown runner image label: %s", job.RunsOn))
+					return
+				}
+
+				containerName := fmt.Sprintf("runner-%s", jobTracker.TaskId)
 
 				logger.Info("Using image %s (label: %s)", runnerImage, job.RunsOn)
 
diff --git a/internal/runner/runner_test.go b/internal/runner/runner_test.go
deleted file mode 100644
index 283eb41..0000000
--- a/internal/runner/runner_test.go
+++ /dev/null
@@ -1,37 +0,0 @@
-package runner
-
-import (
-	"testing"
-)
-
-func TestGetContainerNameReturnsADeterministicName(t *testing.T) {
-	runner := Runner{}
-	containerName := runner.GetContainerName("testid")
-	if containerName != "runner-testid" {
-		t.Errorf("Unexpected container name: %s", containerName)
-	}
-}
-
-func TestGetImageUriByLabelReturnsAUriIfLabelled(t *testing.T) {
-	labels := map[string]string{
-		"test-label": "some-image",
-	}
-	runner := Runner{
-		Labels: labels,
-	}
-	imageUri := runner.GetImageUriByLabel("test-label")
-	if uri, _ := labels["test-label"]; imageUri != uri {
-		t.Errorf("Expected uri %s, got %s instead.", uri, imageUri)
-	}
-}
-
-func TestGetImageUriByLabelReturnsTheDefaultUriIfLabelUnknown(t *testing.T) {
-	labels := map[string]string{}
-	runner := Runner{
-		Labels: labels,
-	}
-	imageUri := runner.GetImageUriByLabel("test-label")
-	if imageUri != "debian:latest" {
-		t.Errorf("Expected default uri, got %s instead.", imageUri)
-	}
-}