diff --git a/H316/h316_defs.h b/H316/h316_defs.h
index a21a7d8a..af051de1 100644
--- a/H316/h316_defs.h
+++ b/H316/h316_defs.h
@@ -175,7 +175,7 @@ typedef struct h316_dib DIB;
 #define INT_V_NODEF     17              /* int not deferred */
 #define INT_V_ON        18              /* int on */
 #define INT_V_EXTD      16              /* first extended interrupt */
-#define INT_V_NONE      -1              /* no interrupt used */
+#define INT_V_NONE      0xffffffff      /* no interrupt used */
 
 /* I/O macros */
 
diff --git a/H316/tests/implloop4.cmd b/H316/tests/implloop4.cmd
new file mode 100644
index 00000000..927713b3
--- /dev/null
+++ b/H316/tests/implloop4.cmd
@@ -0,0 +1,21 @@
+;;  *** IMP LINE FOUR (ONLY!) LOOPBACK TEST ***
+
+; Set the simulator configuration ...
+echo IMP line four loopback test...
+do impconfig.cmd
+SET IMP NUM=2
+
+; Load the IMP code ...
+echo Loading IMP code ...
+do impcode.cmd
+
+; Start up the modem links!
+SET MI1 DISABLED
+SET MI2 DISABLED
+SET MI3 DISABLED
+SET MI4 ENABLED
+DEPOSIT MI4 LLOOP 1
+SET MI5 DISABLED
+
+; And we're done ..
+echo Type GO to start ...
diff --git a/Ibm1130/ibm1130_cr.c b/Ibm1130/ibm1130_cr.c
index 0985a954..427428e7 100644
--- a/Ibm1130/ibm1130_cr.c
+++ b/Ibm1130/ibm1130_cr.c
@@ -887,7 +887,7 @@ static t_stat cp_set_code (UNIT *uptr, int32 match, char *cptr, void *desc)
 	return SCPE_OK;
 }
 
-t_stat load_cr_boot (int drvno, int switches)
+t_stat load_cr_boot (int32 drvno, int switches)
 {
 	int i;
 	char *name, msg[80];
@@ -972,7 +972,7 @@ t_stat load_cr_boot (int drvno, int switches)
 	return SCPE_OK;
 }
 
-t_stat cr_boot (int unitno, DEVICE *dptr)
+t_stat cr_boot (int32 unitno, DEVICE *dptr)
 {
 	t_stat rval;
 	int i;
diff --git a/Ibm1130/ibm1130_defs.h b/Ibm1130/ibm1130_defs.h
index b32012de..f8f32df8 100644
--- a/Ibm1130/ibm1130_defs.h
+++ b/Ibm1130/ibm1130_defs.h
@@ -269,7 +269,7 @@ void xio_t2741_terminal (int32 addr, int32 func, int32 modify);				/* IO selectr
 void xio_error 			(char *msg);
 
 void   bail (char *msg);
-t_stat load_cr_boot (int drv, int switches);
+t_stat load_cr_boot (int32 drv, int switches);
 t_stat cr_boot (int32 unitno, DEVICE *dptr);
 t_stat cr_rewind (void);
 t_stat cr_detach (UNIT *uptr);
diff --git a/Ibm1130/ibm1130_prt.c b/Ibm1130/ibm1130_prt.c
index f6a50fde..61f53995 100644
--- a/Ibm1130/ibm1130_prt.c
+++ b/Ibm1130/ibm1130_prt.c
@@ -649,7 +649,7 @@ static t_stat prt1403_svc(UNIT *uptr)
 
 /* delete_cmd - SCP command to delete a file */
 
-static t_stat delete_cmd (int flag, char *cptr)
+static t_stat delete_cmd (int32 flag, char *cptr)
 {
 	char gbuf[CBUFSIZE];
 	int status;
diff --git a/PDP11/pdp11_dmc.c b/PDP11/pdp11_dmc.c
index 47a1f97c..d2215037 100644
--- a/PDP11/pdp11_dmc.c
+++ b/PDP11/pdp11_dmc.c
@@ -349,7 +349,7 @@ return TRUE;
 
 static void *remqueue (QH *entry)
 {
-if (entry->queue->count <= 0)
+if (entry->queue->count == 0)
     return NULL;
 entry->prev->next = entry->next;
 entry->next->prev = entry->prev;
diff --git a/PDP11/pdp11_kmc.c b/PDP11/pdp11_kmc.c
index d62db266..e34b8490 100644
--- a/PDP11/pdp11_kmc.c
+++ b/PDP11/pdp11_kmc.c
@@ -654,7 +654,7 @@ static void kmc_ctrlIn (int32 k, dupstate *d, int line);
 
 /* Receive functions */
 void kmc_rxBufferIn(dupstate *d, int32 ba, uint32 sel6v);
-static void kdp_receive(int dupidx, int count);
+static void kdp_receive(int32 dupidx, int count);
 
 /* Transmit functions */
 static void kmc_txBufferIn(dupstate *d, int32 ba, uint32 sel6v);
@@ -2036,7 +2036,7 @@ void kmc_rxBufferIn(dupstate *d, int32 ba, uint32 sel6v) {
  * requires them for other modes.
  */
 
-static void kdp_receive(int dupidx, int count) {
+static void kdp_receive(int32 dupidx, int count) {
     int32 k;
     dupstate* d;
     UNIT *rxup;
diff --git a/VAX/vax610_sysdev.c b/VAX/vax610_sysdev.c
index 8aa9d7f3..46164a58 100644
--- a/VAX/vax610_sysdev.c
+++ b/VAX/vax610_sysdev.c
@@ -278,7 +278,7 @@ return;
 struct reglink {                                        /* register linkage */
     uint32      low;                                    /* low addr */
     uint32      high;                                   /* high addr */
-    t_stat      (*read)(int32 pa);                      /* read routine */
+    int32       (*read)(int32 pa);                      /* read routine */
     void        (*write)(int32 pa, int32 val, int32 lnt); /* write routine */
     };
 
diff --git a/sim_ether.c b/sim_ether.c
index 147a358f..4fb0f021 100644
--- a/sim_ether.c
+++ b/sim_ether.c
@@ -3013,7 +3013,7 @@ do {
         u_char buf[ETH_MAX_JUMBO_FRAME];
 
         memset(&header, 0, sizeof(header));
-        len = (int)sim_read_sock (dev->fd_handle, buf, (int32)sizeof(buf));
+        len = (int)sim_read_sock (dev->fd_handle, (char *)buf, (int32)sizeof(buf));
         if (len > 0) {
           status = 1;
           header.caplen = header.len = len;