diff --git a/SourceGen/PlatformSymbols.cs b/SourceGen/PlatformSymbols.cs
index 897e816..3dd86e3 100644
--- a/SourceGen/PlatformSymbols.cs
+++ b/SourceGen/PlatformSymbols.cs
@@ -283,7 +283,7 @@ namespace SourceGen {
                 out string badMaskMsg) {
             Debug.Assert(line.StartsWith(MULTI_MASK_CMD));
             const int MIN = 0;
-            const int MAX = 0x00ffff;
+            const int MAX = 0x00ffffff;
 
             badMaskMsg = Res.Strings.ERR_INVALID_MULTI_MASK;
             multiMask = null;
diff --git a/SourceGen/SGTestData/20170-external-symbols-1.sym65 b/SourceGen/SGTestData/20170-external-symbols-1.sym65
index 8e76ba1..fdec8cd 100644
--- a/SourceGen/SGTestData/20170-external-symbols-1.sym65
+++ b/SourceGen/SGTestData/20170-external-symbols-1.sym65
@@ -1,7 +1,7 @@
 ; Copyright 2019 faddenSoft. All Rights Reserved.
 ; See the LICENSE.txt file for distribution terms (Apache 2.0).
 
-*SYNOPSIS Symbol set 1 for test 2021-external-symbols
+*SYNOPSIS Symbol set 1 for test 20170-external-symbols
 
 ; Platform symbols aren't applied to file data.
 CodeWrap    @   $0f00  $1000    ;encases program
diff --git a/SourceGen/SGTestData/20170-external-symbols-2.sym65 b/SourceGen/SGTestData/20170-external-symbols-2.sym65
index 388ef04..a837c3c 100644
--- a/SourceGen/SGTestData/20170-external-symbols-2.sym65
+++ b/SourceGen/SGTestData/20170-external-symbols-2.sym65
@@ -1,7 +1,7 @@
 ; Copyright 2019 faddenSoft. All Rights Reserved.
 ; See the LICENSE.txt file for distribution terms (Apache 2.0).
 
-*SYNOPSIS Symbol set 2 for test 2021-external-symbols
+*SYNOPSIS Symbol set 2 for test 20170-external-symbols
 
 ; override 2nd and 3rd
 SameName2   @   $2011
diff --git a/SourceGen/SGTestData/20170-external-symbols-3.sym65 b/SourceGen/SGTestData/20170-external-symbols-3.sym65
index c149562..ce753a2 100644
--- a/SourceGen/SGTestData/20170-external-symbols-3.sym65
+++ b/SourceGen/SGTestData/20170-external-symbols-3.sym65
@@ -1,7 +1,7 @@
 ; Copyright 2019 faddenSoft. All Rights Reserved.
 ; See the LICENSE.txt file for distribution terms (Apache 2.0).
 
-*SYNOPSIS Symbol set 3 for test 2021-external-symbols
+*SYNOPSIS Symbol set 3 for test 20170-external-symbols
 
 ; override 3rd
 SameName3   @   $2022
diff --git a/SourceGen/SGTestData/20172-external-symbols b/SourceGen/SGTestData/20172-external-symbols
new file mode 100644
index 0000000..d6bd82d
Binary files /dev/null and b/SourceGen/SGTestData/20172-external-symbols differ
diff --git a/SourceGen/SGTestData/20172-external-symbols.dis65 b/SourceGen/SGTestData/20172-external-symbols.dis65
new file mode 100644
index 0000000..c885001
--- /dev/null
+++ b/SourceGen/SGTestData/20172-external-symbols.dis65
@@ -0,0 +1,63 @@
+### 6502bench SourceGen dis65 v1.0 ###
+{
+"_ContentVersion":4,
+"FileDataLength":258,
+"FileDataCrc32":-1921102947,
+"ProjectProps":{
+"CpuName":"65816",
+"IncludeUndocumentedInstr":false,
+"TwoByteBrk":false,
+"EntryFlags":32702671,
+"AutoLabelStyle":"Simple",
+"AnalysisParams":{
+"AnalyzeUncategorizedData":true,
+"DefaultTextScanMode":"LowHighAscii",
+"MinCharsForString":4,
+"SeekNearbyTargets":true,
+"UseRelocData":false,
+"SmartPlpHandling":false,
+"SmartPlbHandling":true},
+
+"PlatformSymbolFileIdentifiers":["PROJ:20172-external-symbols.sym65"],
+"ExtensionScriptFileIdentifiers":[],
+"ProjectSyms":{
+}},
+
+"AddressMap":[{
+"Offset":0,
+"Addr":4096}],
+"TypeHints":[{
+"Low":0,
+"High":0,
+"Hint":"Code"}],
+"StatusFlagOverrides":{
+},
+
+"Comments":{
+},
+
+"LongComments":{
+},
+
+"Notes":{
+},
+
+"UserLabels":{
+},
+
+"OperandFormats":{
+},
+
+"LvTables":{
+},
+
+"Visualizations":[],
+"VisualizationAnimations":[],
+"VisualizationSets":{
+},
+
+"RelocList":{
+},
+
+"DbrValues":{
+}}
diff --git a/SourceGen/SGTestData/20172-external-symbols.sym65 b/SourceGen/SGTestData/20172-external-symbols.sym65
new file mode 100644
index 0000000..dc3a9d3
--- /dev/null
+++ b/SourceGen/SGTestData/20172-external-symbols.sym65
@@ -0,0 +1,30 @@
+; Copyright 2020 faddenSoft. All Rights Reserved.
+; See the LICENSE.txt file for distribution terms (Apache 2.0).
+
+*SYNOPSIS Symbol set for test 20172-external-symbols
+
+; map 00/Cxxx and 01/Cxxx to 00/Cxxx
+*MULTI_MASK $fef000 $00c000 $000fff
+
+;addr_00     @   $00/c030
+;addr_01     @   $01/c030
+loaddr      @   $c030
+
+; map e0/Cxxx and e1/Cxxx to e0/Cxxx
+*MULTI_MASK $fef000 $e0c000 $000fff
+
+;addr_e0     @   $e0/c030
+;addr_e1     @   $e1/c030
+hiaddr      @   $e0c030
+
+; clear multi-mask
+*MULTI_MASK
+
+addr_02     @   $02/c030
+addr_03     @   $03/c030
+addr_e2     @   $e2/c030
+addr_e3     @   $e3/c030
+
+oth_00      @   $00/1234
+oth_01      @   $01/1234
+oth_02      @   $02/1234
diff --git a/SourceGen/SGTestData/Expected/20172-external-symbols_64tass.S b/SourceGen/SGTestData/Expected/20172-external-symbols_64tass.S
new file mode 100644
index 0000000..03892db
--- /dev/null
+++ b/SourceGen/SGTestData/Expected/20172-external-symbols_64tass.S
@@ -0,0 +1,96 @@
+        .cpu    "65816"
+oth_00  =       $1234
+loaddr  =       $c030
+oth_01  =       $011234
+oth_02  =       $021234
+addr_02 =       $02c030
+addr_03 =       $03c030
+hiaddr  =       $e0c030
+addr_e2 =       $e2c030
+addr_e3 =       $e3c030
+
+*       =       $1000
+        .as
+        .xs
+        clc
+        xce
+        sep     #$30
+        phk
+        plb
+        lda     loaddr
+        lda     loaddr+$10000
+        lda     addr_02
+        lda     addr_03
+        lda     hiaddr
+        lda     hiaddr+$10000
+        lda     addr_e2
+        lda     addr_e3
+        lda     oth_00
+        lda     oth_01
+        lda     oth_02
+        lda     #$01
+        pha
+        plb
+        lda     @lloaddr
+        lda     loaddr
+        lda     addr_02
+        lda     addr_03
+        lda     hiaddr
+        lda     hiaddr+$10000
+        lda     addr_e2
+        lda     addr_e3
+        lda     @loth_00
+        lda     oth_01 & $ffff
+        lda     oth_02
+        lda     #$02
+        pha
+        plb
+        lda     @lloaddr
+        lda     loaddr+$10000
+        lda     addr_02 & $ffff
+        lda     addr_03
+        lda     hiaddr
+        lda     hiaddr+$10000
+        lda     addr_e2
+        lda     addr_e3
+        lda     @loth_00
+        lda     oth_01
+        lda     oth_02 & $ffff
+        lda     #$03
+        pha
+        plb
+        lda     @lloaddr
+        lda     loaddr+$10000
+        lda     addr_02
+        lda     addr_03 & $ffff
+        lda     hiaddr
+        lda     hiaddr+$10000
+        lda     addr_e2
+        lda     addr_e3
+        lda     @loth_00
+        lda     oth_01
+        lda     oth_02
+        lda     #$e0
+        pha
+        plb
+        lda     @lloaddr
+        lda     loaddr+$10000
+        lda     addr_02
+        lda     addr_03
+        lda     hiaddr & $ffff
+        lda     hiaddr+$10000
+        lda     addr_e2
+        lda     addr_e3
+        lda     #$e1
+        pha
+        plb
+        lda     @lloaddr
+        lda     loaddr+$10000
+        lda     addr_02
+        lda     addr_03
+        lda     hiaddr
+        lda     hiaddr & $ffff
+        lda     addr_e2
+        lda     addr_e3
+        rts
+
diff --git a/SourceGen/SGTestData/Expected/20172-external-symbols_acme.S b/SourceGen/SGTestData/Expected/20172-external-symbols_acme.S
new file mode 100644
index 0000000..8d7f082
--- /dev/null
+++ b/SourceGen/SGTestData/Expected/20172-external-symbols_acme.S
@@ -0,0 +1,96 @@
+        !cpu    65816
+oth_00  =       $1234
+loaddr  =       $c030
+oth_01  =       $011234
+oth_02  =       $021234
+addr_02 =       $02c030
+addr_03 =       $03c030
+hiaddr  =       $e0c030
+addr_e2 =       $e2c030
+addr_e3 =       $e3c030
+
+*       =       $1000
+        !as
+        !rs
+        clc
+        xce
+        sep     #$30
+        phk
+        plb
+        lda     loaddr
+        lda+3   loaddr+$10000
+        lda+3   addr_02
+        lda+3   addr_03
+        lda+3   hiaddr
+        lda+3   hiaddr+$10000
+        lda+3   addr_e2
+        lda+3   addr_e3
+        lda     oth_00
+        lda+3   oth_01
+        lda+3   oth_02
+        lda     #$01
+        pha
+        plb
+        lda+3   loaddr
+        lda     loaddr
+        lda+3   addr_02
+        lda+3   addr_03
+        lda+3   hiaddr
+        lda+3   hiaddr+$10000
+        lda+3   addr_e2
+        lda+3   addr_e3
+        lda+3   oth_00
+        lda     oth_01 & $ffff
+        lda+3   oth_02
+        lda     #$02
+        pha
+        plb
+        lda+3   loaddr
+        lda+3   loaddr+$10000
+        lda     addr_02 & $ffff
+        lda+3   addr_03
+        lda+3   hiaddr
+        lda+3   hiaddr+$10000
+        lda+3   addr_e2
+        lda+3   addr_e3
+        lda+3   oth_00
+        lda+3   oth_01
+        lda     oth_02 & $ffff
+        lda     #$03
+        pha
+        plb
+        lda+3   loaddr
+        lda+3   loaddr+$10000
+        lda+3   addr_02
+        lda     addr_03 & $ffff
+        lda+3   hiaddr
+        lda+3   hiaddr+$10000
+        lda+3   addr_e2
+        lda+3   addr_e3
+        lda+3   oth_00
+        lda+3   oth_01
+        lda+3   oth_02
+        lda     #$e0
+        pha
+        plb
+        lda+3   loaddr
+        lda+3   loaddr+$10000
+        lda+3   addr_02
+        lda+3   addr_03
+        lda     hiaddr & $ffff
+        lda+3   hiaddr+$10000
+        lda+3   addr_e2
+        lda+3   addr_e3
+        lda     #$e1
+        pha
+        plb
+        lda+3   loaddr
+        lda+3   loaddr+$10000
+        lda+3   addr_02
+        lda+3   addr_03
+        lda+3   hiaddr
+        lda     hiaddr & $ffff
+        lda+3   addr_e2
+        lda+3   addr_e3
+        rts
+
diff --git a/SourceGen/SGTestData/Expected/20172-external-symbols_cc65.S b/SourceGen/SGTestData/Expected/20172-external-symbols_cc65.S
new file mode 100644
index 0000000..10a64a6
--- /dev/null
+++ b/SourceGen/SGTestData/Expected/20172-external-symbols_cc65.S
@@ -0,0 +1,97 @@
+         .setcpu "65816"
+oth_00   =       $1234
+loaddr   =       $c030
+oth_01   =       $011234
+oth_02   =       $021234
+addr_02  =       $02c030
+addr_03  =       $03c030
+hiaddr   =       $e0c030
+addr_e2  =       $e2c030
+addr_e3  =       $e3c030
+
+;         .segment "SEG000"
+         .org    $1000
+         .a8
+         .i8
+         clc
+         xce
+         sep     #$30
+         phk
+         plb
+         lda     loaddr
+         lda     loaddr+$10000
+         lda     addr_02
+         lda     addr_03
+         lda     hiaddr
+         lda     hiaddr+$10000
+         lda     addr_e2
+         lda     addr_e3
+         lda     oth_00
+         lda     oth_01
+         lda     oth_02
+         lda     #$01
+         pha
+         plb
+         lda     f:loaddr
+         lda     loaddr
+         lda     addr_02
+         lda     addr_03
+         lda     hiaddr
+         lda     hiaddr+$10000
+         lda     addr_e2
+         lda     addr_e3
+         lda     f:oth_00
+         lda     oth_01 & $ffff
+         lda     oth_02
+         lda     #$02
+         pha
+         plb
+         lda     f:loaddr
+         lda     loaddr+$10000
+         lda     addr_02 & $ffff
+         lda     addr_03
+         lda     hiaddr
+         lda     hiaddr+$10000
+         lda     addr_e2
+         lda     addr_e3
+         lda     f:oth_00
+         lda     oth_01
+         lda     oth_02 & $ffff
+         lda     #$03
+         pha
+         plb
+         lda     f:loaddr
+         lda     loaddr+$10000
+         lda     addr_02
+         lda     addr_03 & $ffff
+         lda     hiaddr
+         lda     hiaddr+$10000
+         lda     addr_e2
+         lda     addr_e3
+         lda     f:oth_00
+         lda     oth_01
+         lda     oth_02
+         lda     #$e0
+         pha
+         plb
+         lda     f:loaddr
+         lda     loaddr+$10000
+         lda     addr_02
+         lda     addr_03
+         lda     hiaddr & $ffff
+         lda     hiaddr+$10000
+         lda     addr_e2
+         lda     addr_e3
+         lda     #$e1
+         pha
+         plb
+         lda     f:loaddr
+         lda     loaddr+$10000
+         lda     addr_02
+         lda     addr_03
+         lda     hiaddr
+         lda     hiaddr & $ffff
+         lda     addr_e2
+         lda     addr_e3
+         rts
+
diff --git a/SourceGen/SGTestData/Expected/20172-external-symbols_cc65.cfg b/SourceGen/SGTestData/Expected/20172-external-symbols_cc65.cfg
new file mode 100644
index 0000000..3a1ab21
--- /dev/null
+++ b/SourceGen/SGTestData/Expected/20172-external-symbols_cc65.cfg
@@ -0,0 +1,11 @@
+# 6502bench SourceGen generated linker script for 20172-external-symbols
+MEMORY {
+    MAIN: file=%O, start=%S, size=65536;
+#    MEM000: file=%O, start=$1000, size=258;
+}
+SEGMENTS {
+    CODE: load=MAIN, type=rw;
+#    SEG000: load=MEM000, type=rw;
+}
+FEATURES {}
+SYMBOLS {}
diff --git a/SourceGen/SGTestData/Expected/20172-external-symbols_merlin32.S b/SourceGen/SGTestData/Expected/20172-external-symbols_merlin32.S
new file mode 100644
index 0000000..3d55286
--- /dev/null
+++ b/SourceGen/SGTestData/Expected/20172-external-symbols_merlin32.S
@@ -0,0 +1,93 @@
+oth_00   equ   $1234
+loaddr   equ   $c030
+oth_01   equ   $011234
+oth_02   equ   $021234
+addr_02  equ   $02c030
+addr_03  equ   $03c030
+hiaddr   equ   $e0c030
+addr_e2  equ   $e2c030
+addr_e3  equ   $e3c030
+
+         org   $1000
+         clc
+         xce
+         sep   #$30
+         phk
+         plb
+         lda   loaddr
+         ldal  loaddr+$10000
+         ldal  addr_02
+         ldal  addr_03
+         ldal  hiaddr
+         ldal  hiaddr+$10000
+         ldal  addr_e2
+         ldal  addr_e3
+         lda   oth_00
+         ldal  oth_01
+         ldal  oth_02
+         lda   #$01
+         pha
+         plb
+         ldal  loaddr
+         lda   loaddr
+         ldal  addr_02
+         ldal  addr_03
+         ldal  hiaddr
+         ldal  hiaddr+$10000
+         ldal  addr_e2
+         ldal  addr_e3
+         ldal  oth_00
+         lda   oth_01
+         ldal  oth_02
+         lda   #$02
+         pha
+         plb
+         ldal  loaddr
+         ldal  loaddr+$10000
+         lda   addr_02
+         ldal  addr_03
+         ldal  hiaddr
+         ldal  hiaddr+$10000
+         ldal  addr_e2
+         ldal  addr_e3
+         ldal  oth_00
+         ldal  oth_01
+         lda   oth_02
+         lda   #$03
+         pha
+         plb
+         ldal  loaddr
+         ldal  loaddr+$10000
+         ldal  addr_02
+         lda   addr_03
+         ldal  hiaddr
+         ldal  hiaddr+$10000
+         ldal  addr_e2
+         ldal  addr_e3
+         ldal  oth_00
+         ldal  oth_01
+         ldal  oth_02
+         lda   #$e0
+         pha
+         plb
+         ldal  loaddr
+         ldal  loaddr+$10000
+         ldal  addr_02
+         ldal  addr_03
+         lda   hiaddr
+         ldal  hiaddr+$10000
+         ldal  addr_e2
+         ldal  addr_e3
+         lda   #$e1
+         pha
+         plb
+         ldal  loaddr
+         ldal  loaddr+$10000
+         ldal  addr_02
+         ldal  addr_03
+         ldal  hiaddr
+         lda   hiaddr
+         ldal  addr_e2
+         ldal  addr_e3
+         rts
+
diff --git a/SourceGen/SGTestData/Source/20172-external-symbols.S b/SourceGen/SGTestData/Source/20172-external-symbols.S
new file mode 100644
index 0000000..b884cc6
--- /dev/null
+++ b/SourceGen/SGTestData/Source/20172-external-symbols.S
@@ -0,0 +1,118 @@
+; Copyright 2020 faddenSoft. All Rights Reserved.
+; See the LICENSE.txt file for distribution terms (Apache 2.0).
+;
+; Assembler: Merlin 32
+
+; EDIT: set up a pair of MULTI_MASKs for 00/01 and e0/e1
+
+addr_00 equ     $00c030
+addr_01 equ     $01c030
+addr_02 equ     $02c030
+addr_03 equ     $03c030
+
+addr_e0 equ     $e0c030
+addr_e1 equ     $e1c030
+addr_e2 equ     $e2c030
+addr_e3 equ     $e3c030
+
+oth_00  equ     $001234
+oth_01  equ     $011234
+oth_02  equ     $021234
+
+        org     $1000
+
+        clc
+        xce
+        sep     #$30
+        mx      %11
+
+; bank 00
+        phk
+        plb
+        lda:    addr_00
+        ldal    addr_01
+        ldal    addr_02
+        ldal    addr_03
+        ldal    addr_e0
+        ldal    addr_e1
+        ldal    addr_e2
+        ldal    addr_e3
+        lda:    oth_00
+        ldal    oth_01
+        ldal    oth_02
+
+; bank 01
+        lda     #$01
+        pha
+        plb
+        ldal    addr_00
+        lda:    addr_01
+        ldal    addr_02
+        ldal    addr_03
+        ldal    addr_e0
+        ldal    addr_e1
+        ldal    addr_e2
+        ldal    addr_e3
+        ldal    oth_00
+        lda:    oth_01
+        ldal    oth_02
+
+; bank 02
+        lda     #$02
+        pha
+        plb
+        ldal    addr_00
+        ldal    addr_01
+        lda:    addr_02
+        ldal    addr_03
+        ldal    addr_e0
+        ldal    addr_e1
+        ldal    addr_e2
+        ldal    addr_e3
+        ldal    oth_00
+        ldal    oth_01
+        lda:    oth_02
+
+; bank 03
+        lda     #$03
+        pha
+        plb
+        ldal    addr_00
+        ldal    addr_01
+        ldal    addr_02
+        lda:    addr_03
+        ldal    addr_e0
+        ldal    addr_e1
+        ldal    addr_e2
+        ldal    addr_e3
+        ldal    oth_00
+        ldal    oth_01
+        ldal    oth_02
+
+; bank e0
+        lda     #$e0
+        pha
+        plb
+        ldal    addr_00
+        ldal    addr_01
+        ldal    addr_02
+        ldal    addr_03
+        lda:    addr_e0
+        ldal    addr_e1
+        ldal    addr_e2
+        ldal    addr_e3
+
+; bank e1
+        lda     #$e1
+        pha
+        plb
+        ldal    addr_00
+        ldal    addr_01
+        ldal    addr_02
+        ldal    addr_03
+        ldal    addr_e0
+        lda:    addr_e1
+        ldal    addr_e2
+        ldal    addr_e3
+
+END     rts