diff -pruN 2.1.3.1-2/debian/changelog 2.1.3.1-2.1/debian/changelog
--- 2.1.3.1-2/debian/changelog	2021-08-17 13:01:12.000000000 +0000
+++ 2.1.3.1-2.1/debian/changelog	2025-10-27 14:21:30.000000000 +0000
@@ -1,3 +1,10 @@
+diffpdf (2.1.3.1-2.1) unstable; urgency=medium
+
+  * Non-maintainer upload.
+  * Fix FTBFS with CMake 4. (Closes: #1112844)
+
+ -- Adrian Bunk <bunk@debian.org>  Mon, 27 Oct 2025 16:21:30 +0200
+
 diffpdf (2.1.3.1-2) unstable; urgency=medium
 
   * Wrap long lines in changelog entries: 2.1.3.1-1.
diff -pruN 2.1.3.1-2/debian/patches/cmake-4.patch 2.1.3.1-2.1/debian/patches/cmake-4.patch
--- 2.1.3.1-2/debian/patches/cmake-4.patch	1970-01-01 00:00:00.000000000 +0000
+++ 2.1.3.1-2.1/debian/patches/cmake-4.patch	2025-10-27 14:21:30.000000000 +0000
@@ -0,0 +1,12 @@
+Description: Fix FTBFS with CMake 4
+Author: Adrian Bunk <bunk@debian.org>
+Bug-Debian: https://bugs.debian.org/1112844
+
+--- diffpdf-2.1.3.1.orig/CMakeLists.txt
++++ diffpdf-2.1.3.1/CMakeLists.txt
+@@ -1,4 +1,4 @@
+-cmake_minimum_required(VERSION 3.1)
++cmake_minimum_required(VERSION 3.5)
+ 
+ set(DIFFPDF_VERSION 2.1.3.1)
+ project(DiffPDF VERSION ${DIFFPDF_VERSION})
diff -pruN 2.1.3.1-2/debian/patches/series 2.1.3.1-2.1/debian/patches/series
--- 2.1.3.1-2/debian/patches/series	2021-05-06 17:50:33.000000000 +0000
+++ 2.1.3.1-2.1/debian/patches/series	2025-10-27 14:21:30.000000000 +0000
@@ -4,3 +4,4 @@
 0006-do-not-check-extension.patch
 0007-desktop.patch
 0008-cmake-OpenMP.patch
+cmake-4.patch