diff --git a/files/er_safe_run.sh b/files/er_safe_run.sh
index e4b053a..2de5f91 100755
--- a/files/er_safe_run.sh
+++ b/files/er_safe_run.sh
@@ -1,3 +1,5 @@
 #!/bin/bash
 
-flock -w 3600 /var/lib/elastic-recheck/er_safe_run.lock $@
+# Timeout after 4 hours as we've seen this script occasionally fail to
+# exit after running for days.
+flock -w 3600 timeout -k 60 14400 /var/lib/elastic-recheck/er_safe_run.lock $@