diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 80b0d0c5ded6..d28b8270a1f8 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -3981,10 +3981,10 @@ BufferIsPermanent(Buffer buffer)
 XLogRecPtr
 BufferGetLSNAtomic(Buffer buffer)
 {
-	BufferDesc *bufHdr = GetBufferDescriptor(buffer - 1);
 	char	   *page = BufferGetPage(buffer);
 	XLogRecPtr	lsn;
 	uint32		buf_state;
+	BufferDesc *bufHdr;
 
 	/*
 	 * If we don't need locking for correctness, fastpath out.
@@ -3996,6 +3996,7 @@ BufferGetLSNAtomic(Buffer buffer)
 	Assert(BufferIsValid(buffer));
 	Assert(BufferIsPinned(buffer));
 
+	bufHdr = GetBufferDescriptor(buffer - 1);
 	buf_state = LockBufHdr(bufHdr);
 	lsn = PageGetLSN(page);
 	UnlockBufHdr(bufHdr, buf_state);