diff --git a/AltairZ80/mfdc.c b/AltairZ80/mfdc.c
index 14c1edaf..a1a36fc2 100644
--- a/AltairZ80/mfdc.c
+++ b/AltairZ80/mfdc.c
@@ -241,7 +241,7 @@ static t_stat mfdc_reset(DEVICE *dptr)
 static t_stat mfdc_attach(UNIT *uptr, CONST char *cptr)
 {
     t_stat r;
-    unsigned int i = 0;
+    int32 i = 0;
 
     r = attach_unit(uptr, cptr);    /* attach unit  */
     if ( r != SCPE_OK)              /* error?       */