diff --git a/gnome-system-monitor-c99.patch b/gnome-system-monitor-c99.patch
new file mode 100644
index 0000000..b8e765c
--- /dev/null
+++ b/gnome-system-monitor-c99.patch
@@ -0,0 +1,53 @@
+Submitted upstream:
+
+  <https://gitlab.gnome.org/GNOME/gnome-system-monitor/-/merge_requests/67>
+
+Author: Florian Weimer <fweimer@redhat.com>
+Date:   Mon Feb 6 08:36:22 2023 +0100
+
+    meson: Remove unused ctime_r check
+    
+    It did not work because of an implicit function declaration
+    (<time.h> does not declare ctime_r due to -std=c11, which disables
+    GNU extensions).  The only use of CTIME_R_THREE_ARGS was #if'ed out,
+    so remove that as well.
+
+diff --git a/meson.build b/meson.build
+index a314a684b2a9ceb4..985a361a60b08240 100644
+--- a/meson.build
++++ b/meson.build
+@@ -105,16 +105,6 @@ add_project_arguments(cx.get_supported_arguments(cxxflags),
+ 
+ conf.set('HAVE_LKSTRFTIME', cc.has_function('strftime'))
+ 
+-conf.set('CTIME_R_THREE_ARGS', cc.compiles('''
+-#include <time.h>
+-int main() {
+-  char *buf;
+-  time_t date;
+-  ctime_r (&date, buf, 100);
+-}
+-'''))
+-
+-
+ configure_file(
+   output: 'config.h',
+   configuration: conf,
+diff --git a/src/legacy/e_date.c b/src/legacy/e_date.c
+index 2697e892c7463357..71d0b5214b6d15cf 100644
+--- a/src/legacy/e_date.c
++++ b/src/legacy/e_date.c
+@@ -194,13 +194,6 @@ filter_date (time_t date)
+             e_utf8_strftime_fix_am_pm (buf, 26, _("%b %d %Y"), &then);
+         }
+     }
+-#if 0
+-#ifdef CTIME_R_THREE_ARGS
+-    ctime_r (&date, buf, 26);
+-#else
+-    ctime_r (&date, buf);
+-#endif
+-#endif
+ 
+     return g_strdup (buf);
+ }
diff --git a/gnome-system-monitor.spec b/gnome-system-monitor.spec
index 1018638..72911d7 100644
--- a/gnome-system-monitor.spec
+++ b/gnome-system-monitor.spec
@@ -5,12 +5,13 @@
 
 Name:           gnome-system-monitor
 Version:        42.0
-Release:        3%{?dist}
+Release:        4%{?dist}
 Summary:        Process and resource monitor
 
 License:        GPLv2+
 URL:            https://wiki.gnome.org/Apps/SystemMonitor
 Source0:        https://download.gnome.org/sources/%{name}/42/%{name}-%{tarball_version}.tar.xz
+Patch0: gnome-system-monitor-c99.patch
 
 BuildRequires:  gcc
 BuildRequires:  gcc-c++
@@ -68,6 +69,9 @@ desktop-file-validate $RPM_BUILD_ROOT%{_datadir}/applications/gnome-system-monit
 %{_libexecdir}/gnome-system-monitor/
 
 %changelog
+* Mon Feb 06 2023 Florian Weimer <fweimer@redhat.com> - 42.0-4
+- Fix C99 compatibility issue
+
 * Thu Jan 19 2023 Fedora Release Engineering <releng@fedoraproject.org> - 42.0-3
 - Rebuilt for https://fedoraproject.org/wiki/Fedora_38_Mass_Rebuild