diff --git a/src/hw.mockingboard.a b/src/hw.mockingboard.a
index 148e455db..19be8f486 100644
--- a/src/hw.mockingboard.a
+++ b/src/hw.mockingboard.a
@@ -56,8 +56,22 @@ GetMockingboardStuff
          sta   MAGIC_Z80_LOCATION, x
          dex
          bpl   -
-         stx   $C403                 ; enable Mockingboard 4C support
+
+         lda   $C405
+         cmp   #$38
+         bne   @not_mouse
+         lda   $C407
+         cmp   #$18
+         beq   @use_slot5            ; looks like the mouse
+
+@not_mouse
+         stx   $C403                 ; enable Mockingboard 4C support in slot 4
          stx   $C404
+         bne   @not_iic              ; always
+
+@use_slot5
+         stx   $C503                 ; try enable Mockingboard 4C support in slot 5 instead
+         stx   $C504
 
 @not_iic
          lda   #$00