diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index eb3c516058f..ce78ac413ef 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5454,7 +5454,7 @@ StartupXLOG(void)
 
 		/* Copy the valid part of the last block, and zero the rest */
 		page = &XLogCtl->pages[firstIdx * XLOG_BLCKSZ];
-		memcpy(page, endOfRecoveryInfo->lastPage, XLOG_BLCKSZ);
+		memcpy(page, endOfRecoveryInfo->lastPage, len);
 		memset(page + len, 0, XLOG_BLCKSZ - len);
 
 		XLogCtl->xlblocks[firstIdx] = endOfRecoveryInfo->lastPageBeginPtr + XLOG_BLCKSZ;