diff --git a/tools/reaper/README.md b/tools/reaper/README.md
index 8dcca14..34a6d42 100644
--- a/tools/reaper/README.md
+++ b/tools/reaper/README.md
@@ -37,6 +37,8 @@ compute.googleapis.com/InstanceTemplate: gke-flux-test-full-dove-default-pool-42
 compute.googleapis.com/InstanceTemplate: gke-flux-test-full-dove-default-pool-dcded0bb
 container.googleapis.com/Cluster: flux-test-full-dove
 artifactregistry.googleapis.com/Repository: projects/darkowlzz-gcp/locations/us-central1/repositories/flux-test-full-dove
+2023/11/04 00:49:45 resources found but not deleted
+exit status 1
 ```
 
 JSON output is also supported:
diff --git a/tools/reaper/main.go b/tools/reaper/main.go
index eb58608..3c26b10 100644
--- a/tools/reaper/main.go
+++ b/tools/reaper/main.go
@@ -205,6 +205,11 @@ func main() {
 				}
 			}
 		}
+	} else if !*delete && len(resources) > 0 {
+		// Exit with non-zero exit code when resources are found but not
+		// deleted. This is to help detect stale resources when run in CI by
+		// failing the job.
+		log.Fatal("resources found but not deleted")
 	}
 }