diff -pruN 5.15.19+dfsg2-1/debian/changelog 5.15.19+dfsg2-2/debian/changelog
--- 5.15.19+dfsg2-1/debian/changelog	2025-09-20 13:16:17.000000000 +0000
+++ 5.15.19+dfsg2-2/debian/changelog	2025-12-08 07:52:16.000000000 +0000
@@ -1,3 +1,10 @@
+qtwebengine-opensource-src (5.15.19+dfsg2-2) unstable; urgency=medium
+
+  * Add a patch from Arch Linux to fix build with ICU 78 (closes: #1121677,
+    #1122105).
+
+ -- Dmitry Shachnev <mitya57@debian.org>  Mon, 08 Dec 2025 10:52:16 +0300
+
 qtwebengine-opensource-src (5.15.19+dfsg2-1) unstable; urgency=medium
 
   * Exclude minizip/src/doc from the tarball (closes: #1115475).
diff -pruN 5.15.19+dfsg2-1/debian/patches/icu-78.patch 5.15.19+dfsg2-2/debian/patches/icu-78.patch
--- 5.15.19+dfsg2-1/debian/patches/icu-78.patch	1970-01-01 00:00:00.000000000 +0000
+++ 5.15.19+dfsg2-2/debian/patches/icu-78.patch	2025-12-08 07:52:16.000000000 +0000
@@ -0,0 +1,19 @@
+Description: fix build with ICU 78
+Origin: Arch Linux, https://aur.archlinux.org/cgit/aur.git/tree/qt5-webengine-icu-78.patch?h=qt5-webengine
+ The proper fix would be cherry-picking this commit
+ https://chromium.googlesource.com/chromium/src/+/f62990fb134b7e61
+ and a commit to support ICU 78 on top of that, but upstream Chromium
+ does not support ICU 78 yet.
+Last-Update: 2025-12-07
+
+--- a/src/3rdparty/chromium/third_party/blink/renderer/platform/text/text_break_iterator.cc
++++ b/src/3rdparty/chromium/third_party/blink/renderer/platform/text/text_break_iterator.cc
+@@ -163,7 +163,7 @@ static const unsigned char kAsciiLineBre
+ // clang-format on
+ 
+ #if U_ICU_VERSION_MAJOR_NUM >= 74
+-#define BA_LB_COUNT (U_LB_COUNT - 8)
++#define BA_LB_COUNT (40) /* (U_LB_COUNT - 8) */
+ #elif U_ICU_VERSION_MAJOR_NUM >= 58
+ #define BA_LB_COUNT (U_LB_COUNT - 3)
+ #else
diff -pruN 5.15.19+dfsg2-1/debian/patches/series 5.15.19+dfsg2-2/debian/patches/series
--- 5.15.19+dfsg2-1/debian/patches/series	2025-09-20 13:16:17.000000000 +0000
+++ 5.15.19+dfsg2-2/debian/patches/series	2025-12-08 07:52:16.000000000 +0000
@@ -26,3 +26,4 @@ build-with-c++17.patch
 ninja-1.12.patch
 mips64el-v8-regexp.patch
 gcc-15.patch
+icu-78.patch