diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c
index 395e75f768f..f1112111de8 100644
--- a/src/backend/commands/vacuum.c
+++ b/src/backend/commands/vacuum.c
@@ -1712,13 +1712,6 @@ vacuum_rel(Oid relid, RangeVar *relation, VacuumParams *params)
 	/* Begin a transaction for vacuuming this relation */
 	StartTransactionCommand();
 
-	/*
-	 * Need to acquire a snapshot to prevent pg_subtrans from being truncated,
-	 * cutoff xids in local memory wrapping around, and to have updated xmin
-	 * horizons.
-	 */
-	PushActiveSnapshot(GetTransactionSnapshot());
-
 	if (!(params->options & VACOPT_FULL))
 	{
 		/*
@@ -1739,9 +1732,11 @@ vacuum_rel(Oid relid, RangeVar *relation, VacuumParams *params)
 		 * Note: these flags remain set until CommitTransaction or
 		 * AbortTransaction.  We don't want to clear them until we reset
 		 * MyProc->xid/xmin, otherwise GetOldestNonRemovableTransactionId()
-		 * might appear to go backwards, which is probably Not Good.
+		 * might appear to go backwards, which is probably Not Good.  (We also
+		 * set PROC_IN_VACUUM *before* taking our own snapshot, so that our
+		 * xmin doesn't become visible ahead of setting the flag.)
 		 */
-		LWLockAcquire(ProcArrayLock, LW_SHARED);
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
 		MyProc->statusFlags |= PROC_IN_VACUUM;
 		if (params->is_wraparound)
 			MyProc->statusFlags |= PROC_VACUUM_FOR_WRAPAROUND;
@@ -1749,6 +1744,13 @@ vacuum_rel(Oid relid, RangeVar *relation, VacuumParams *params)
 		LWLockRelease(ProcArrayLock);
 	}
 
+	/*
+	 * Need to acquire a snapshot to prevent pg_subtrans from being truncated,
+	 * cutoff xids in local memory wrapping around, and to have updated xmin
+	 * horizons.
+	 */
+	PushActiveSnapshot(GetTransactionSnapshot());
+
 	/*
 	 * Check for user-requested abort.  Note we want this to be inside a
 	 * transaction, so xact.c doesn't issue useless WARNING.
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index 4324e326565..f1f4df7d70f 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -181,7 +181,7 @@ StartupDecodingContext(List *output_plugin_options,
 	 */
 	if (!IsTransactionOrTransactionBlock())
 	{
-		LWLockAcquire(ProcArrayLock, LW_SHARED);
+		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
 		MyProc->statusFlags |= PROC_IN_LOGICAL_DECODING;
 		ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
 		LWLockRelease(ProcArrayLock);
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index 94edb24b22d..ee912b9d5e4 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -662,10 +662,8 @@ ProcArrayEndTransaction(PGPROC *proc, TransactionId latestXid)
 		/* avoid unnecessarily dirtying shared cachelines */
 		if (proc->statusFlags & PROC_VACUUM_STATE_MASK)
 		{
-			/* Only safe to change my own flags with just share lock */
-			Assert(proc == MyProc);
 			Assert(!LWLockHeldByMe(ProcArrayLock));
-			LWLockAcquire(ProcArrayLock, LW_SHARED);
+			LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
 			Assert(proc->statusFlags == ProcGlobal->statusFlags[proc->pgxactoff]);
 			proc->statusFlags &= ~PROC_VACUUM_STATE_MASK;
 			ProcGlobal->statusFlags[proc->pgxactoff] = proc->statusFlags;
@@ -685,8 +683,8 @@ ProcArrayEndTransactionInternal(PGPROC *proc, TransactionId latestXid)
 	size_t		pgxactoff = proc->pgxactoff;
 
 	/*
-	 * Note: we need exclusive lock here because we're going to
-	 * change other processes' PGPROC entries.
+	 * Note: we need exclusive lock here because we're going to change other
+	 * processes' PGPROC entries.
 	 */
 	Assert(LWLockHeldByMeInMode(ProcArrayLock, LW_EXCLUSIVE));
 	Assert(TransactionIdIsValid(ProcGlobal->xids[pgxactoff]));
diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h
index e75f6e81782..e77f76ae8a1 100644
--- a/src/include/storage/proc.h
+++ b/src/include/storage/proc.h
@@ -102,9 +102,9 @@ typedef enum
  * but its myProcLocks[] lists are valid.
  *
  * We allow many fields of this struct to be accessed without locks, such as
- * statusFlags or delayChkpt. However, keep in mind that writing mirrored ones
- * (see below) requires holding ProcArrayLock or XidGenLock in at least shared
- * mode, so that pgxactoff does not change concurrently.
+ * delayChkpt and isBackgroundWorker. However, keep in mind that writing
+ * mirrored ones (see below) requires holding ProcArrayLock or XidGenLock in
+ * at least shared mode, so that pgxactoff does not change concurrently.
  *
  * Mirrored fields:
  *