diff --git a/qt5-qtwebengine-c99.patch b/qt5-qtwebengine-c99.patch
new file mode 100644
index 0000000..bf34288
--- /dev/null
+++ b/qt5-qtwebengine-c99.patch
@@ -0,0 +1,45 @@
+Avoid calls to the undeclared strlcpy function in libsync.  This
+prevents a build failure with future compilers.
+
+Submitted upstream: <https://bugreports.qt.io/browse/QTBUG-111440>
+
+diff -up qtwebengine-everywhere-src-5.15.12/src/3rdparty/chromium/third_party/libsync/BUILD.gn.c99 qtwebengine-everywhere-src-5.15.12/src/3rdparty/chromium/third_party/libsync/BUILD.gn
+--- qtwebengine-everywhere-src-5.15.12/src/3rdparty/chromium/third_party/libsync/BUILD.gn.c99	2023-02-23 10:54:15.909380015 +0100
++++ qtwebengine-everywhere-src-5.15.12/src/3rdparty/chromium/third_party/libsync/BUILD.gn	2023-02-23 11:00:32.019601795 +0100
+@@ -21,24 +21,15 @@ if (!use_system_libsync) {
+     ]
+   }
+ 
+-  config("libsync_private_config") {
+-    # To suppress the warning caused by strlcpy.
+-    cflags = [ "-Wno-implicit-function-declaration" ]
+-  }
+-
+   source_set("libsync") {
+     sources = [
+       "src/include/sync/sync.h",
+       "src/sw_sync.h",
+       "src/sync.c",
+-      "strlcpy.c",
+     ]
+ 
+     configs -= [ "//build/config/compiler:chromium_code" ]
+-    configs += [
+-      "//build/config/compiler:no_chromium_code",
+-      ":libsync_private_config",
+-    ]
++    configs += [ "//build/config/compiler:no_chromium_code" ]
+ 
+     public_configs = [ ":libsync_config" ]
+   }
+diff -up qtwebengine-everywhere-src-5.15.12/src/3rdparty/chromium/third_party/libsync/src/sync.c.c99 qtwebengine-everywhere-src-5.15.12/src/3rdparty/chromium/third_party/libsync/src/sync.c
+--- qtwebengine-everywhere-src-5.15.12/src/3rdparty/chromium/third_party/libsync/src/sync.c.c99	2023-02-23 10:54:30.650231820 +0100
++++ qtwebengine-everywhere-src-5.15.12/src/3rdparty/chromium/third_party/libsync/src/sync.c	2023-02-23 10:54:50.116036131 +0100
+@@ -29,6 +29,7 @@
+ 
+ #include <sync/sync.h>
+ 
++#include "../strlcpy.c"
+ 
+ struct sw_sync_create_fence_data {
+   __u32 value;
diff --git a/qt5-qtwebengine.spec b/qt5-qtwebengine.spec
index 876d346..0d24632 100644
--- a/qt5-qtwebengine.spec
+++ b/qt5-qtwebengine.spec
@@ -62,7 +62,7 @@
 Summary: Qt5 - QtWebEngine components
 Name:    qt5-qtwebengine
 Version: 5.15.12
-Release: 3%{?dist}
+Release: 4%{?dist}
 
 # See LICENSE.GPL LICENSE.LGPL LGPL_EXCEPTION.txt, for details
 # See also http://qt-project.org/doc/qt-5.0/qtdoc/licensing.html
@@ -119,6 +119,7 @@ Patch32: qtwebengine-skia-missing-includes.patch
 ## From: https://chromium-review.googlesource.com/c/chromium/src/+/3545665
 Patch33: qtwebengine-5.15-Backport-of-16k-page-support-on-aarch64.patch
 Patch34: qtwebengine-fix-build.patch
+Patch35: qt5-qtwebengine-c99.patch
 
 ## Upstream patches:
 
@@ -451,6 +452,8 @@ popd
 %patch33 -p1 -b .aarch64-16kb-support
 %patch34 -p1 -b .fix-build
 
+%patch35 -p1 -b .c99
+
 # delete all "toolprefix = " lines from build/toolchain/linux/BUILD.gn, as we
 # never cross-compile in native Fedora RPMs, fixes ARM and aarch64 FTBFS
 sed -i -e '/toolprefix = /d' -e 's/\${toolprefix}//g' \
@@ -675,6 +678,9 @@ done
 
 
 %changelog
+* Thu Feb 23 2023 Florian Weimer <fweimer@redhat.com> - 5.15.12-4
+- Port bundled libsync to C99 (#2155642)
+
 * Wed Feb 15 2023 Tom Callaway <spot@fedoraproject.org> - 5.15.12-3
 - rebuild for libvpx