diff --git a/zsnes/src/cfg.psr b/zsnes/src/cfg.psr
index 023afc1d..d618a593 100644
--- a/zsnes/src/cfg.psr
+++ b/zsnes/src/cfg.psr
@@ -352,6 +352,7 @@ NEWSYM MovieVideoMode, db 4
 NEWSYM MovieAudio, db 1
 NEWSYM MovieVideoAudio, db 0
 NEWSYM MovieAudioCompress, db 0
+NEWSYM TwelveHourClock, db 0
 NEWSYM NTSCFilter, db 0
 NEWSYM NTSCBlend, db 0
 NEWSYM NTSCHue, db 0
diff --git a/zsnes/src/gui/gui.asm b/zsnes/src/gui/gui.asm
index 1386c11a..04a72cac 100644
--- a/zsnes/src/gui/gui.asm
+++ b/zsnes/src/gui/gui.asm
@@ -141,7 +141,7 @@ EXTSYM GUIEnableTransp,FilteredGUI,MouseWheel,TrapMouseCursor,AlwaysOnTop
 EXTSYM pl1p209,pl1p209b,SaveMainWindowPos,FastFwdToggle,SidewinderFix,RaisePitch
 EXTSYM KeyDisplayBatt,PauseFocusChange,KeyIncreaseGamma,KeyDecreaseGamma
 EXTSYM MovieVideoMode, MovieAudio,MovieVideoAudio,MovieAudioCompress
-EXTSYM device1,device2
+EXTSYM device1,device2,TwelveHourClock
 
 %ifdef __UNIXSDL__
 EXTSYM numlockptr
diff --git a/zsnes/src/gui/guikeys.inc b/zsnes/src/gui/guikeys.inc
index b8a42f70..b172a9b2 100644
--- a/zsnes/src/gui/guikeys.inc
+++ b/zsnes/src/gui/guikeys.inc
@@ -788,6 +788,7 @@ GUIOptionKeys:
   GUIKeyCheckbox FPSAtStart,'F'
   GUIKeyCheckbox Turbo30hz,'E'
   GUIKeyCheckbox TimerEnable,'C'
+  GUIKeyCheckbox TwelveHourClock,'1'
   GUIKeyCheckbox OldGfxMode2,'O'
   GUIKeyCheckbox DontSavePath,'D'
   GUIKeyCheckbox SmallMsgText,'S'
diff --git a/zsnes/src/gui/guimouse.inc b/zsnes/src/gui/guimouse.inc
index 94c27cd4..aa60afae 100644
--- a/zsnes/src/gui/guimouse.inc
+++ b/zsnes/src/gui/guimouse.inc
@@ -2392,6 +2392,7 @@ DisplayGUIOptionClick:
   GUIClickCButton 11,70,byte[FPSAtStart]
   GUIClickCButton 11,80,byte[Turbo30hz]
   GUIClickCButton 11,90,byte[TimerEnable]
+  GUIClickCButton 130,90,byte[TwelveHourClock]
   GUIClickCButtonO 11,100,byte[OldGfxMode2]
   GUIClickCButton 11,110,byte[DontSavePath]
   GUIClickCButton 11,120,byte[SmallMsgText]
diff --git a/zsnes/src/gui/guiwindp.inc b/zsnes/src/gui/guiwindp.inc
index 20e0b873..6335c5cb 100644
--- a/zsnes/src/gui/guiwindp.inc
+++ b/zsnes/src/gui/guiwindp.inc
@@ -1606,6 +1606,7 @@ DisplayGUIOption:       ; Emu Options
   GUIDisplayCheckboxu 4,11,70,FPSAtStart,GUIOptionText7,0
   GUIDisplayCheckboxu 4,11,80,Turbo30hz,GUIOptionText8,2
   GUIDisplayCheckboxu 4,11,90,TimerEnable,GUIOptionText9,12
+  GUIDisplayCheckboxu 4,130,90,TwelveHourClock,GUIOptionText9a,0
   GUIDisplayCheckboxu 4,11,100,OldGfxMode2,GUIOptionTextA,0
   GUIDisplayCheckboxu 4,11,110,DontSavePath,GUIOptionTextB,0
   GUIDisplayCheckboxu 4,11,120,SmallMsgText,GUIOptionTextC,1
@@ -1629,6 +1630,7 @@ GUIOptionText6b db 'HIGH PRIORITY MODE',0
 GUIOptionText7 db 'FPS AT PROGRAM START',0
 GUIOptionText8 db 'USE 30HZ FOR TURBO',0
 GUIOptionText9 db 'ENABLE GAME CLOCK',0
+GUIOptionText9a db '12HR',0
 GUIOptionTextA db 'OLD GFX MODE 2',0
 GUIOptionTextB db 'DON',39,'T SAVE CUR PATH',0
 GUIOptionTextC db 'USE SMALL MESSAGE TEXT',0
diff --git a/zsnes/src/video/procvid.asm b/zsnes/src/video/procvid.asm
index 6e5a190e..99d810c5 100644
--- a/zsnes/src/video/procvid.asm
+++ b/zsnes/src/video/procvid.asm
@@ -2667,6 +2667,7 @@ NEWSYM tempoffset, resw 1
 NEWSYM Testval, resd 1
 SECTION .text
 
+EXTSYM TwelveHourClock
 
 NEWSYM ClockOutput
     cmp byte[cbitmode],1
@@ -2733,6 +2734,10 @@ NEWSYM ClockOutput
     call .output
     pop eax
     ; eax = hours
+    cmp byte[TwelveHourClock],1
+    jne .no12hour
+    sub eax,12
+.no12hour
     xor edx,edx
     mov ebx,10
     div ebx