diff --git a/builder/bootloader.py b/builder/bootloader.py
index fbd9680..0c9eb89 100644
--- a/builder/bootloader.py
+++ b/builder/bootloader.py
@@ -124,12 +124,15 @@ def get_bootloader_dxcore(framework_dir, board_config):
     UPLOADBOOTCMD="$BOOTUPLOADER $BOOTUPLOADERFLAGS $UPLOAD_FLAGS $BOOTFLAGS",
 )
 
-if not env.BoardConfig().get("upload", {}).get("require_upload_port", False):
+if env.subst("$UPLOAD_PROTOCOL") in (
+    "jtag2updi",
+    "serialupdi",
+) or env.BoardConfig().get("upload", {}).get("require_upload_port", False):
+    env.AutodetectUploadPort()
+    env.Append(BOOTUPLOADERFLAGS=["-P", '"$UPLOAD_PORT"'])
+else:
     # upload methods via USB
     env.Append(BOOTUPLOADERFLAGS=["-P", "usb"])
-else:
-    env.AutodetectUploadPort()
-    env.Append(FUSESUPLOADERFLAGS=["-P", '"$UPLOAD_PORT"'])
 
 if env.subst("$UPLOAD_PROTOCOL") != "custom":
     env.Append(BOOTUPLOADERFLAGS=["-c", "$UPLOAD_PROTOCOL"])