diff --git a/hw/fdc.c b/hw/fdc.c
index 4b06e04..f8af2de 100644
--- a/hw/fdc.c
+++ b/hw/fdc.c
@@ -434,6 +434,7 @@
     FDCtrl *fdctrl = opaque;
     uint32_t retval;
 
+    reg &= 7;
     switch (reg) {
     case FD_REG_SRA:
         retval = fdctrl_read_statusA(fdctrl);
@@ -471,6 +472,7 @@
 
     FLOPPY_DPRINTF("write reg%d: 0x%02x\n", reg & 7, value);
 
+    reg &= 7;
     switch (reg) {
     case FD_REG_DOR:
         fdctrl_write_dor(fdctrl, value);