diff --git a/blockjob.c b/blockjob.c
index ae9c5b2925..bcd7efcb64 100644
--- a/blockjob.c
+++ b/blockjob.c
@@ -99,6 +99,9 @@ void block_job_completed(BlockJob *job, int ret)
     BlockDriverState *bs = job->bs;
 
     assert(bs->job == job);
+    assert(!job->completed);
+    job->completed = true;
+    job->ret = ret;
     job->cb(job->opaque, ret);
     block_job_unref(job);
 }
diff --git a/include/block/blockjob.h b/include/block/blockjob.h
index ed856d72bf..c70d55a644 100644
--- a/include/block/blockjob.h
+++ b/include/block/blockjob.h
@@ -153,6 +153,15 @@ struct BlockJob {
 
     /** Reference count of the block job */
     int refcnt;
+
+    /* True if this job has reported completion by calling block_job_completed.
+     */
+    bool completed;
+
+    /* ret code passed to block_job_completed.
+     */
+    int ret;
+
 };
 
 /**