diff --git a/NEWS b/NEWS
index eccb0ed..ceadacd 100644
--- a/NEWS
+++ b/NEWS
@@ -2,6 +2,13 @@ News for the tz database
 
 Unreleased, experimental changes
 
+  Changes affecting past time stamps
+
+    Asia/Phnom_Penh and Asia/Vientiane have been turned into links, as
+    they differed from existing zones only for older time stamps.  As
+    usual, these changes affect pre-1970 time stamps only.  Their old
+    contents have been moved to the 'backzone' file.
+
   Changes affecting code
 
     If USG_COMPAT is defined and the requested time stamp is standard time,
diff --git a/asia b/asia
index 0be896b..ea03e3f 100644
--- a/asia
+++ b/asia
@@ -271,12 +271,8 @@ Zone	Asia/Rangoon	6:24:40 -	LMT	1880        # or Yangon
 			6:30	-	MMT	# Myanmar Time
 
 # Cambodia
-# Zone	NAME		GMTOFF	RULES	FORMAT	[UNTIL]
-Zone	Asia/Phnom_Penh	6:59:40 -	LMT	1906 Jun  9
-			7:06:20	-	SMT	1911 Mar 11  0:01 # Saigon MT?
-			7:00	-	ICT	1912 May
-			8:00	-	ICT	1931 May
-			7:00	-	ICT
+# See Asia/Bangkok.
+
 
 # China
 
@@ -1714,12 +1710,8 @@ Zone	Asia/Kuwait	3:11:56 -	LMT	1950
 			3:00	-	AST
 
 # Laos
-# Zone	NAME		GMTOFF	RULES	FORMAT	[UNTIL]
-Zone	Asia/Vientiane	6:50:24 -	LMT	1906 Jun  9       # or Viangchan
-			7:06:20	-	SMT	1911 Mar 11  0:01 # Saigon MT?
-			7:00	-	ICT	1912 May
-			8:00	-	ICT	1931 May
-			7:00	-	ICT
+# See Asia/Bangkok.
+
 
 # Lebanon
 # Rule	NAME	FROM	TO	TYPE	IN	ON	AT	SAVE	LETTER/S
@@ -2732,6 +2724,8 @@ Zone	Asia/Dushanbe	4:35:12 -	LMT	1924 May  2
 Zone	Asia/Bangkok	6:42:04	-	LMT	1880
 			6:42:04	-	BMT	1920 Apr # Bangkok Mean Time
 			7:00	-	ICT
+Link Asia/Bangkok Asia/Phnom_Penh	# Cambodia
+Link Asia/Bangkok Asia/Vientiane	# Laos
 
 # Turkmenistan
 # From Shanks & Pottenger.
diff --git a/backzone b/backzone
index f464131..7bb79f3 100644
--- a/backzone
+++ b/backzone
@@ -353,11 +353,25 @@ Zone	Asia/Kashgar	5:03:56	-	LMT	1928     # or Kashi or Kaxgar
 # Portuguese India switched to GMT+5 on 1912-01-01.
 #Zone	Asia/Panaji	[not enough info to complete]
 
+# Cambodia
+Zone	Asia/Phnom_Penh	6:59:40 -	LMT	1906 Jun  9
+			7:06:20	-	SMT	1911 Mar 11  0:01 # Saigon MT?
+			7:00	-	ICT	1912 May
+			8:00	-	ICT	1931 May
+			7:00	-	ICT
+
 # Israel
 Zone	Asia/Tel_Aviv	2:19:04 -	LMT	1880
 			2:21	-	JMT	1918
 			2:00	Zion	I%sT
 
+# Laos
+Zone	Asia/Vientiane	6:50:24 -	LMT	1906 Jun  9       # or Viangchan
+			7:06:20	-	SMT	1911 Mar 11  0:01 # Saigon MT?
+			7:00	-	ICT	1912 May
+			8:00	-	ICT	1931 May
+			7:00	-	ICT
+
 # Jan Mayen
 # From Whitman:
 Zone Atlantic/Jan_Mayen	-1:00	-	EGT
diff --git a/checktab.awk b/checktab.awk
index 84c49ff..3da1e9b 100644
--- a/checktab.awk
+++ b/checktab.awk
@@ -28,8 +28,6 @@ BEGIN {
 	  tztab["Asia/Ho_Chi_Minh"] = 1
 	  tztab["Asia/Kuwait"] = 1
 	  tztab["Asia/Muscat"] = 1
-	  tztab["Asia/Phnom_Penh"] = 1
-	  tztab["Asia/Vientiane"] = 1
 	  tztab["Indian/Antananarivo"] = 1
 	  tztab["Indian/Comoro"] = 1
 	  tztab["Indian/Mayotte"] = 1