diff -pruN 1.9.0+ds-2/debian/changelog 1.9.0+ds-2.1/debian/changelog
--- 1.9.0+ds-2/debian/changelog	2021-09-30 18:54:11.000000000 +0000
+++ 1.9.0+ds-2.1/debian/changelog	2025-10-26 09:23:00.000000000 +0000
@@ -1,3 +1,10 @@
+birdtray (1.9.0+ds-2.1) unstable; urgency=medium
+
+  * Non-maintainer upload.
+  * Backport upstream fix for FTBFS with CMake 4. (Closes: #1112755)
+
+ -- Adrian Bunk <bunk@debian.org>  Sun, 26 Oct 2025 11:23:00 +0200
+
 birdtray (1.9.0+ds-2) unstable; urgency=medium
 
   * Update the watch file.
diff -pruN 1.9.0+ds-2/debian/patches/0001-Bump-minimum-required-CMake-version.patch 1.9.0+ds-2.1/debian/patches/0001-Bump-minimum-required-CMake-version.patch
--- 1.9.0+ds-2/debian/patches/0001-Bump-minimum-required-CMake-version.patch	1970-01-01 00:00:00.000000000 +0000
+++ 1.9.0+ds-2.1/debian/patches/0001-Bump-minimum-required-CMake-version.patch	2025-10-26 08:49:07.000000000 +0000
@@ -0,0 +1,22 @@
+From 8b1dbf95db5485ce19350ea957f7ffcfa369aa5b Mon Sep 17 00:00:00 2001
+From: Abestanis <abestanis.gc@gmail.com>
+Date: Fri, 18 Apr 2025 05:35:40 +0200
+Subject: Bump minimum required CMake version
+
+---
+ CMakeLists.txt | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/CMakeLists.txt b/CMakeLists.txt
+index 22394ad..160bb80 100644
+--- a/CMakeLists.txt
++++ b/CMakeLists.txt
+@@ -1,4 +1,4 @@
+-cmake_minimum_required(VERSION 3.1.0)
++cmake_minimum_required(VERSION 3.5)
+ 
+ if(POLICY CMP0092)
+     cmake_policy(SET CMP0092 NEW)
+-- 
+2.30.2
+
diff -pruN 1.9.0+ds-2/debian/patches/series 1.9.0+ds-2.1/debian/patches/series
--- 1.9.0+ds-2/debian/patches/series	1970-01-01 00:00:00.000000000 +0000
+++ 1.9.0+ds-2.1/debian/patches/series	2025-10-26 09:21:32.000000000 +0000
@@ -0,0 +1 @@
+0001-Bump-minimum-required-CMake-version.patch