diff --git a/tools/pio_upload_port.py b/tools/pio_upload_port.py
index cd66b77..0e94c81 100644
--- a/tools/pio_upload_port.py
+++ b/tools/pio_upload_port.py
@@ -62,6 +62,10 @@ def query_id(port, timeout=5):
 
 
 def detect_port(source, target, env):
+    if env.subst("$UPLOAD_PORT"):
+        print(f"  Upload port already set to {env.subst('$UPLOAD_PORT')}, skipping auto-detect")
+        return
+
     env_name = env.subst("$PIOENV")
     expected_id = ENV_TO_ID.get(env_name)