diff --git a/pytest-embedded-idf/pytest_embedded_idf/serial.py b/pytest-embedded-idf/pytest_embedded_idf/serial.py
index 4d168b62..0d644a54 100644
--- a/pytest-embedded-idf/pytest_embedded_idf/serial.py
+++ b/pytest-embedded-idf/pytest_embedded_idf/serial.py
@@ -156,7 +156,7 @@ def flash(self, app: Optional[IdfApp] = None) -> None:
                 elif v:
                     _args.append(f'--{k}')
             else:
-                _args.append(f'--{k}')
+                _args.append(f'--{k.replace("_", "-")}')
                 if k == 'after':
                     _args.append('hard_reset')
                 else: