diff --git a/Gui.py b/Gui.py
index d2eb545b..5cd51868 100755
--- a/Gui.py
+++ b/Gui.py
@@ -88,6 +88,9 @@ def guiMain(args=None):
     balancingVar = IntVar()
     balancingVar.set(1) #set default
     balancingCheckbutton = Checkbutton(checkBoxFrame, text="Multiworld Progression Balancing", variable=balancingVar)
+    extendedmsuVar = IntVar()
+    extendedmsuVar.set(0) #set default
+    extendedmsuCheckbutton = Checkbutton(checkBoxFrame, text="Extended MSU", variable=extendedmsuVar)
     createSpoilerCheckbutton.pack(expand=True, anchor=W)
     suppressRomCheckbutton.pack(expand=True, anchor=W)
     openpyramidCheckbutton.pack(expand=True, anchor=W)
@@ -102,6 +105,7 @@ def guiMain(args=None):
     hintsCheckbutton.pack(expand=True, anchor=W)
     customCheckbutton.pack(expand=True, anchor=W)
     balancingCheckbutton.pack(expand=True, anchor=W)
+    extendedmsuCheckbutton.pack(expand=True, anchor=W)
 
     romOptionsFrame = LabelFrame(rightHalfFrame, text="Rom options")
     romOptionsFrame.columnconfigure(0, weight=1)
@@ -438,6 +442,7 @@ def guiMain(args=None):
         guiargs.item_functionality = itemfunctionVar.get()
         guiargs.timer = timerVar.get()
         guiargs.skip_progression_balancing = not balancingVar.get()
+        guiargs.extendedmsu = extendedmsuVar.get()
         if guiargs.timer == "none":
             guiargs.timer = False
         guiargs.dungeon_counters = dungeonCounterVar.get()
diff --git a/Rom.py b/Rom.py
index cb8505c2..795b1738 100644
--- a/Rom.py
+++ b/Rom.py
@@ -22,7 +22,8 @@ from EntranceShuffle import door_addresses
 
 
 JAP10HASH = '03a63945398191337e896e5771f77173'
-# RANDOMIZERBASEHASH = '1907d4caccffe60fc69940cfa11b2dab'
+RANDOMIZERBASEHASH = '1347ce535618fa1a844d2d45cf0ca661'
+EXTENDEDMSURANDOMIZERBASEHASH = 'f42949bde03ba5ea71c2d43a21f5d6bf'
 
 
 class JsonRom(object):
@@ -121,10 +122,10 @@ class LocalRom(object):
                     self.write_bytes(int(baseaddress), values)
 
         # verify md5
-        # patchedmd5 = hashlib.md5()
-        # patchedmd5.update(self.buffer)
-        # if RANDOMIZERBASEHASH != patchedmd5.hexdigest():
-        #     raise RuntimeError('Provided Base Rom unsuitable for patching. Please provide a JAP(1.0) "Zelda no Densetsu - Kamigami no Triforce (Japan).sfc" rom to use as a base.')
+        patchedmd5 = hashlib.md5()
+        patchedmd5.update(self.buffer)
+        if patchedmd5.hexdigest() not in [RANDOMIZERBASEHASH, EXTENDEDMSURANDOMIZERBASEHASH]:
+            raise RuntimeError('Provided Base Rom unsuitable for patching. Please provide a JAP(1.0) "Zelda no Densetsu - Kamigami no Triforce (Japan).sfc" rom to use as a base.')
 
     def write_crc(self):
         crc = (sum(self.buffer[:0x7FDC] + self.buffer[0x7FE0:]) + 0x01FE) & 0xFFFF