diff --git a/src/apple2/bank.c b/src/apple2/bank.c
index 5d4688b..6ee081f 100644
--- a/src/apple2/bank.c
+++ b/src/apple2/bank.c
@@ -245,13 +245,13 @@ SEGMENT_WRITER(apple2_bank_switch_write)
         // Turn on auxiliary memory for zero page + stack
         case 0xC008:
             apple2_set_bank_switch(mach,
-                                   mach->bank_switch | BANK_ALTZP);
+                                   mach->bank_switch & ~BANK_ALTZP);
             break;
 
         // Disable auxiliary memory for zero page + stack
         case 0xC009:
             apple2_set_bank_switch(mach,
-                                   mach->bank_switch & ~BANK_ALTZP);
+                                   mach->bank_switch | BANK_ALTZP);
             break;
     }
 }