diff --git a/frontpanel/FrontPanelTest.c b/frontpanel/FrontPanelTest.c
index 95d27736..97f60078 100644
--- a/frontpanel/FrontPanelTest.c
+++ b/frontpanel/FrontPanelTest.c
@@ -804,8 +804,14 @@ while (1) {
                 printf("%s\n", history);
             }
         else if (match_command ("DEBUG ", cmd, &arg)) {
-            if (sim_panel_device_debug_mode (panel, arg, 1, NULL))
-                printf("Error setting debug mode: %s\n", sim_panel_get_error ());
+            if (arg[0] == '-') {
+                if (sim_panel_device_debug_mode (panel, NULL, 1, arg))
+                    printf("Error setting debug mode: %s\n", sim_panel_get_error ());
+                }
+            else {
+                if (sim_panel_device_debug_mode (panel, arg, 1, NULL))
+                    printf("Error setting debug mode: %s\n", sim_panel_get_error ());
+                }
             }
         else if ((match_command ("EXIT", cmd, NULL)) || (match_command ("QUIT", cmd, NULL)))
             goto Done;
diff --git a/sim_frontpanel.c b/sim_frontpanel.c
index 8cfb6bcd..e6a3ab92 100644
--- a/sim_frontpanel.c
+++ b/sim_frontpanel.c
@@ -1792,8 +1792,9 @@ if (!panel || (panel->State == Error)) {
     sim_panel_set_error (NULL, "Invalid Panel");
     return -1;
     }
-if (_panel_sendf (panel, &cmd_stat, &response, "SHOW %s", device) ||
-    (cmd_stat)) {
+if ((device != NULL) &&
+    ((_panel_sendf (panel, &cmd_stat, &response, "SHOW %s", device) ||
+     (cmd_stat)))) {
     sim_panel_set_error (NULL, "Can't %s Debug Mode: '%s' on Device '%s': %s", 
                                set_unset ? "Enable" : "Disable", mode_bits ? mode_bits : "", device, response);
     free (response);
@@ -1802,7 +1803,7 @@ if (_panel_sendf (panel, &cmd_stat, &response, "SHOW %s", device) ||
 free (response);
 response = NULL;
 if (_panel_sendf (panel, &cmd_stat, &response, "%sDEBUG %s %s", 
-                         set_unset ? "" : "NO", device, mode_bits ? mode_bits : "") ||
+                         set_unset ? "" : "NO", device ? device : "", mode_bits ? mode_bits : "") ||
     (cmd_stat)) {
     sim_panel_set_error (NULL, "Can't %s Debug Mode: '%s' on Device '%s': %s", 
                                set_unset ? "Enable" : "Disable", mode_bits ? mode_bits : "", device, response);