diff --git a/prometheus/defaults/main.yml b/prometheus/defaults/main.yml
index 939e3cffeeca12571d333a708600a17fca325e3a..150dc1930f02cc796dd6cdd5e0731cbcdc154a09 100644
--- a/prometheus/defaults/main.yml
+++ b/prometheus/defaults/main.yml
@@ -2,5 +2,8 @@
 prometheus_args: ""
 prometheus:
   rules:
-    alert:
-    recording:
+    # These variables intentionally left null.  They need to exist, so that the
+    # template works, but they need to have a value (empty string does not
+    # work).
+    alert: null
+    recording: null