diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
index 21f5e2ce95..639bd716b1 100644
--- a/src/backend/postmaster/autovacuum.c
+++ b/src/backend/postmaster/autovacuum.c
@@ -212,9 +212,9 @@ typedef struct autovac_table
  * wi_launchtime Time at which this worker was launched
  * wi_cost_*	Vacuum cost-based delay parameters current in this worker
  *
- * All fields are protected by AutovacuumLock, except for wi_tableoid which is
- * protected by AutovacuumScheduleLock (which is read-only for everyone except
- * that worker itself).
+ * All fields are protected by AutovacuumLock, except for wi_tableoid and
+ * wi_sharedrel which are protected by AutovacuumScheduleLock (note these
+ * two fields are read-only for everyone except that worker itself).
  *-------------
  */
 typedef struct WorkerInfoData
@@ -2317,7 +2317,9 @@ do_autovacuum(void)
 	foreach(cell, table_oids)
 	{
 		Oid			relid = lfirst_oid(cell);
+		HeapTuple	classTup;
 		autovac_table *tab;
+		bool		isshared;
 		bool		skipit;
 		int			stdVacuumCostDelay;
 		int			stdVacuumCostLimit;
@@ -2342,9 +2344,23 @@ do_autovacuum(void)
 		}
 
 		/*
-		 * hold schedule lock from here until we're sure that this table still
-		 * needs vacuuming.  We also need the AutovacuumLock to walk the
-		 * worker array, but we'll let go of that one quickly.
+		 * Find out whether the table is shared or not.  (It's slightly
+		 * annoying to fetch the syscache entry just for this, but in typical
+		 * cases it adds little cost because table_recheck_autovac would
+		 * refetch the entry anyway.  We could buy that back by copying the
+		 * tuple here and passing it to table_recheck_autovac, but that
+		 * increases the odds of that function working with stale data.)
+		 */
+		classTup = SearchSysCache1(RELOID, ObjectIdGetDatum(relid));
+		if (!HeapTupleIsValid(classTup))
+			continue;			/* somebody deleted the rel, forget it */
+		isshared = ((Form_pg_class) GETSTRUCT(classTup))->relisshared;
+		ReleaseSysCache(classTup);
+
+		/*
+		 * Hold schedule lock from here until we've claimed the table.  We
+		 * also need the AutovacuumLock to walk the worker array, but that one
+		 * can just be a shared lock.
 		 */
 		LWLockAcquire(AutovacuumScheduleLock, LW_EXCLUSIVE);
 		LWLockAcquire(AutovacuumLock, LW_SHARED);
@@ -2380,6 +2396,16 @@ do_autovacuum(void)
 			continue;
 		}
 
+		/*
+		 * Store the table's OID in shared memory before releasing the
+		 * schedule lock, so that other workers don't try to vacuum it
+		 * concurrently.  (We claim it here so as not to hold
+		 * AutovacuumScheduleLock while rechecking the stats.)
+		 */
+		MyWorkerInfo->wi_tableoid = relid;
+		MyWorkerInfo->wi_sharedrel = isshared;
+		LWLockRelease(AutovacuumScheduleLock);
+
 		/*
 		 * Check whether pgstat data still says we need to vacuum this table.
 		 * It could have changed if something else processed the table while
@@ -2396,18 +2422,13 @@ do_autovacuum(void)
 		if (tab == NULL)
 		{
 			/* someone else vacuumed the table, or it went away */
+			LWLockAcquire(AutovacuumScheduleLock, LW_EXCLUSIVE);
+			MyWorkerInfo->wi_tableoid = InvalidOid;
+			MyWorkerInfo->wi_sharedrel = false;
 			LWLockRelease(AutovacuumScheduleLock);
 			continue;
 		}
 
-		/*
-		 * Ok, good to go.  Store the table in shared memory before releasing
-		 * the lock so that other workers don't vacuum it concurrently.
-		 */
-		MyWorkerInfo->wi_tableoid = relid;
-		MyWorkerInfo->wi_sharedrel = tab->at_sharedrel;
-		LWLockRelease(AutovacuumScheduleLock);
-
 		/*
 		 * Remember the prevailing values of the vacuum cost GUCs.  We have to
 		 * restore these at the bottom of the loop, else we'll compute wrong
@@ -2522,10 +2543,10 @@ deleted:
 		 * settings, so we don't want to give up our share of I/O for a very
 		 * short interval and thereby thrash the global balance.
 		 */
-		LWLockAcquire(AutovacuumLock, LW_EXCLUSIVE);
+		LWLockAcquire(AutovacuumScheduleLock, LW_EXCLUSIVE);
 		MyWorkerInfo->wi_tableoid = InvalidOid;
 		MyWorkerInfo->wi_sharedrel = false;
-		LWLockRelease(AutovacuumLock);
+		LWLockRelease(AutovacuumScheduleLock);
 
 		/* restore vacuum cost GUCs for the next iteration */
 		VacuumCostDelay = stdVacuumCostDelay;