diff --git a/src/core/job.c b/src/core/job.c
index 826ef6809c..af47987938 100644
--- a/src/core/job.c
+++ b/src/core/job.c
@@ -237,6 +237,7 @@ Job* job_install(Job *j) {
         }
 
         /* Install the job */
+        assert(!*pj);
         *pj = j;
         j->installed = true;