diff --git a/buildroot/share/scripts/upload.py b/buildroot/share/scripts/upload.py
index ee48af6fc6..9fb927c426 100644
--- a/buildroot/share/scripts/upload.py
+++ b/buildroot/share/scripts/upload.py
@@ -157,7 +157,7 @@ def Upload(source, target, env):
     marlin_string_config_h_author = _GetMarlinEnv(MarlinEnv, 'STRING_CONFIG_H_AUTHOR')
 
     # Get firmware upload params
-    upload_firmware_source_name = env['PROGNAME'] + '.bin' if env['PROGNAME'] else str(source[0])
+    upload_firmware_source_name = env['PROGNAME'] + '.bin' if 'PROGNAME' in env else str(source[0])
                                                     # Source firmware filename
     upload_speed = env['UPLOAD_SPEED'] if 'UPLOAD_SPEED' in env else 115200
                                                     # baud rate of serial connection