From 08687aff215a3d5111869a928406f2b289a6fa55 Mon Sep 17 00:00:00 2001
From: gicking <icking@onlinehome.de>
Date: Mon, 26 Jan 2026 12:22:11 +0100
Subject: [PATCH] fix: SoftwareSerial flush() issue

Fixes #2904.

Signed-off-by: gicking <icking@onlinehome.de>
---
 libraries/SoftwareSerial/src/SoftwareSerial.cpp | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/libraries/SoftwareSerial/src/SoftwareSerial.cpp b/libraries/SoftwareSerial/src/SoftwareSerial.cpp
index 6a8c303c6c..20285fc6de 100644
--- a/libraries/SoftwareSerial/src/SoftwareSerial.cpp
+++ b/libraries/SoftwareSerial/src/SoftwareSerial.cpp
@@ -409,6 +409,8 @@ void SoftwareSerial::flush()
   noInterrupts();
   _receive_buffer_head = _receive_buffer_tail = 0;
   interrupts();
+  // wait for previous transmit to complete
+  while (active_out);
 }
 
 int SoftwareSerial::peek()