diff --git a/AltairZ80/altairz80_sys.c b/AltairZ80/altairz80_sys.c
index 2c239175..6e526027 100644
--- a/AltairZ80/altairz80_sys.c
+++ b/AltairZ80/altairz80_sys.c
@@ -952,3 +952,19 @@ t_stat show_iobase(FILE *st, UNIT *uptr, int32 val, CONST void *desc)
     return SCPE_OK;
 }
 
+/* find_unit_index   find index of a unit
+
+   Inputs:
+        uptr    =       pointer to unit
+   Outputs:
+        result  =       index of device
+*/
+int32 find_unit_index(UNIT* uptr)
+{
+    DEVICE *dptr = find_dev_from_unit(uptr);
+
+    if (dptr == NULL)
+        return -1;
+
+    return (uptr - dptr->units);
+}
diff --git a/AltairZ80/i8272.c b/AltairZ80/i8272.c
index 7e1bb4b7..cd8161bd 100644
--- a/AltairZ80/i8272.c
+++ b/AltairZ80/i8272.c
@@ -129,6 +129,7 @@ extern t_stat set_iobase(UNIT *uptr, int32 val, CONST char *cptr, void *desc);
 extern t_stat show_iobase(FILE *st, UNIT *uptr, int32 val, CONST void *desc);
 extern uint32 sim_map_resource(uint32 baseaddr, uint32 size, uint32 resource_type,
                                int32 (*routine)(const int32, const int32, const int32), const char* name, uint8 unmap);
+extern int32 find_unit_index(UNIT* uptr);
 
 /* These are needed for DMA.  PIO Mode has not been implemented yet. */
 extern void PutByteDMA(const uint32 Addr, const uint32 Value);
@@ -166,7 +167,6 @@ extern uint8 GetByteDMA(const uint32 Addr);
 static void raise_i8272_interrupt(void);
 static int32 i8272dev(const int32 port, const int32 io, const int32 data);
 static t_stat i8272_reset(DEVICE *dptr);
-int32 find_unit_index (UNIT *uptr);
 static const char* i8272_description(DEVICE *dptr);
 
 I8272_INFO i8272_info_data = { { 0x0, 0, 0xC0, 2 } };
@@ -243,32 +243,6 @@ static t_stat i8272_reset(DEVICE *dptr)
 }
 
 
-/* find_unit_index   find index of a unit
-
-   Inputs:
-        uptr    =       pointer to unit
-   Outputs:
-        result  =       index of device
-*/
-int32 find_unit_index (UNIT *uptr)
-{
-    DEVICE *dptr;
-    uint32 i;
-
-    if (uptr == NULL)
-        return (-1);
-    dptr = find_dev_from_unit(uptr);
-    for(i=0; i<dptr->numunits; i++) {
-        if(dptr->units + i == uptr) {
-            break;
-        }
-    }
-    if(i == dptr->numunits) {
-        return (-1);
-    }
-    return (i);
-}
-
 /* Attach routine */
 t_stat i8272_attach(UNIT *uptr, CONST char *cptr)
 {