diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c
index d1738c65f5..caefff41e2 100644
--- a/src/backend/storage/lmgr/proc.c
+++ b/src/backend/storage/lmgr/proc.c
@@ -1325,20 +1325,22 @@ ProcSleep(LOCALLOCK *locallock, LockMethod lockMethodTable)
 				int			pid = autovac->pid;
 				StringInfoData locktagbuf;
 				StringInfoData logbuf;	/* errdetail for server log */
+				LOCKTAG		locktag_copy;
+
+				/* release lock as quickly as possible */
+				locktag_copy = lock->tag;
+				LWLockRelease(ProcArrayLock);
 
 				initStringInfo(&locktagbuf);
 				initStringInfo(&logbuf);
-				DescribeLockTag(&locktagbuf, &lock->tag);
+				DescribeLockTag(&locktagbuf, &locktag_copy);
 				appendStringInfo(&logbuf,
 								 _("Process %d waits for %s on %s."),
 								 MyProcPid,
-								 GetLockmodeName(lock->tag.locktag_lockmethodid,
+								 GetLockmodeName(locktag_copy.locktag_lockmethodid,
 												 lockmode),
 								 locktagbuf.data);
 
-				/* release lock as quickly as possible */
-				LWLockRelease(ProcArrayLock);
-
 				/* send the autovacuum worker Back to Old Kent Road */
 				ereport(DEBUG1,
 						(errmsg("sending cancel to blocking autovacuum PID %d",