diff --git a/web/application.js b/web/application.js
index 56ba385f..89d8fb9b 100644
--- a/web/application.js
+++ b/web/application.js
@@ -147,6 +147,7 @@ $(function() {
         case '/gpio':
         case '/debugging':
         case '/firmware':
+            $('firmware-warn').show();
         case '/reset':
             $('#system-link').addClass('active');
             break;
diff --git a/web/upload.html b/web/upload.html
index 4b95147b..1d9fe31b 100644
--- a/web/upload.html
+++ b/web/upload.html
@@ -13,6 +13,12 @@
                 </div>
             </div>
         </div>
+        <div id="firmware-warn" style="display: none;">
+            <br/>
+            <div class="alert alert-danger">
+                WARNING: Units powered over M-bus must be connected to an external power supply during firmware upload. Failure to do so may cause power-down during upload resulting in non-functioning unit.
+            </div>
+        </div>
     </div>
     <hr/>
     <div class="row form-group">