diff --git a/memmap.cpp b/memmap.cpp
index 6a21050c..f7973066 100644
--- a/memmap.cpp
+++ b/memmap.cpp
@@ -1871,9 +1871,9 @@ bool8 CMemory::LoadMultiCartInt ()
     if(Multi.cartType == 4 && Multi.cartOffsetA == 0) { // try to load bios from file
         Multi.cartOffsetA = 0x40000;
         if(Multi.cartSizeA)
-            memmove(ROM + Multi.cartOffsetA,ROM,Multi.cartOffsetB - Multi.cartOffsetA);
-        else // clear cart A so the bios can detect that it's not present
-            memset(ROM,0,Multi.cartOffsetB);
+            memmove(ROM + Multi.cartOffsetA, ROM, Multi.cartSizeA + Multi.cartSizeB);
+        else if(Multi.cartOffsetB) // clear cart A so the bios can detect that it's not present
+            memset(ROM, 0, Multi.cartOffsetB);
         
         FILE	*fp;
 	    size_t	size;