diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index a29246ac23..50fb17e9b3 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.233 2006/04/04 22:39:59 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.234 2006/04/05 03:34:05 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1265,6 +1265,7 @@ AdvanceXLInsertBuffer(void)
 
 		NewLongPage->xlp_sysid = ControlFile->system_identifier;
 		NewLongPage->xlp_seg_size = XLogSegSize;
+		NewLongPage->xlp_xlog_blcksz = XLOG_BLCKSZ;
 		NewPage   ->xlp_info |= XLP_LONG_HEADER;
 
 		Insert->currpos = ((char *) NewPage) +SizeOfXLogLongPHD;
@@ -2994,6 +2995,13 @@ ValidXLOGHeader(XLogPageHeader hdr, int emode)
 					 errdetail("Incorrect XLOG_SEG_SIZE in page header.")));
 			return false;
 		}
+		if (longhdr->xlp_xlog_blcksz != XLOG_BLCKSZ)
+		{
+			ereport(emode,
+					(errmsg("WAL file is from different system"),
+					 errdetail("Incorrect XLOG_BLCKSZ in page header.")));
+			return false;
+		}
 	}
 	recaddr.xlogid = readId;
 	recaddr.xrecoff = readSeg * XLogSegSize + readOff;
@@ -3838,6 +3846,7 @@ BootStrapXLOG(void)
 	longpage = (XLogLongPageHeader) page;
 	longpage->xlp_sysid = sysidentifier;
 	longpage->xlp_seg_size = XLogSegSize;
+	longpage->xlp_xlog_blcksz = XLOG_BLCKSZ;
 
 	/* Insert the initial checkpoint record */
 	record = (XLogRecord *) ((char *) page + SizeOfXLogLongPHD);
diff --git a/src/bin/pg_resetxlog/pg_resetxlog.c b/src/bin/pg_resetxlog/pg_resetxlog.c
index 89ba857a78..4797f0a127 100644
--- a/src/bin/pg_resetxlog/pg_resetxlog.c
+++ b/src/bin/pg_resetxlog/pg_resetxlog.c
@@ -23,7 +23,7 @@
  * Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/bin/pg_resetxlog/pg_resetxlog.c,v 1.42 2006/04/04 22:39:59 tgl Exp $
+ * $PostgreSQL: pgsql/src/bin/pg_resetxlog/pg_resetxlog.c,v 1.43 2006/04/05 03:34:05 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -723,6 +723,7 @@ WriteEmptyXLOG(void)
 	longpage = (XLogLongPageHeader) page;
 	longpage->xlp_sysid = ControlFile.system_identifier;
 	longpage->xlp_seg_size = XLogSegSize;
+	longpage->xlp_xlog_blcksz = XLOG_BLCKSZ;
 
 	/* Insert the initial checkpoint record */
 	record = (XLogRecord *) ((char *) page + SizeOfXLogLongPHD);
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 6fbda53f39..430f57efa8 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -11,7 +11,7 @@
  * Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/access/xlog_internal.h,v 1.12 2006/04/03 23:35:04 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/access/xlog_internal.h,v 1.13 2006/04/05 03:34:05 tgl Exp $
  */
 #ifndef XLOG_INTERNAL_H
 #define XLOG_INTERNAL_H
@@ -69,7 +69,7 @@ typedef struct XLogContRecord
 /*
  * Each page of XLOG file has a header like this:
  */
-#define XLOG_PAGE_MAGIC 0xD05D	/* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD05E	/* can be used as WAL version indicator */
 
 typedef struct XLogPageHeaderData
 {
@@ -93,6 +93,7 @@ typedef struct XLogLongPageHeaderData
 	XLogPageHeaderData std;		/* standard header fields */
 	uint64		xlp_sysid;		/* system identifier from pg_control */
 	uint32		xlp_seg_size;	/* just as a cross-check */
+	uint32		xlp_xlog_blcksz;	/* just as a cross-check */
 } XLogLongPageHeaderData;
 
 #define SizeOfXLogLongPHD	MAXALIGN(sizeof(XLogLongPageHeaderData))