diff --git a/src/basic/calendarspec.c b/src/basic/calendarspec.c
index fd780227732..3918428a576 100644
--- a/src/basic/calendarspec.c
+++ b/src/basic/calendarspec.c
@@ -581,7 +581,8 @@ static int calendarspec_from_time_t(CalendarSpec *c, time_t time) {
         CalendarComponent *year = NULL, *month = NULL, *day = NULL, *hour = NULL, *minute = NULL, *us = NULL;
         int r;
 
-        assert_se(gmtime_r(&time, &tm));
+        if (!gmtime_r(&time, &tm))
+                return -ERANGE;
 
         r = const_chain(tm.tm_year + 1900, &year);
         if (r < 0)
diff --git a/test/fuzz-regressions/fuzz-unit-file/oss-fuzz-6886 b/test/fuzz-regressions/fuzz-unit-file/oss-fuzz-6886
new file mode 100644
index 00000000000..1fbe5ffd99e
--- /dev/null
+++ b/test/fuzz-regressions/fuzz-unit-file/oss-fuzz-6886
@@ -0,0 +1,3 @@
+timer
+[Timer]
+OnCalendar=@88588582097858858
\ No newline at end of file
diff --git a/test/fuzz-regressions/meson.build b/test/fuzz-regressions/meson.build
index 9753c61882f..ee00bcd0469 100644
--- a/test/fuzz-regressions/meson.build
+++ b/test/fuzz-regressions/meson.build
@@ -31,4 +31,5 @@ fuzz_regression_tests = '''
         fuzz-dns-packet/issue-7888
         fuzz-unit-file/oss-fuzz-6884
         fuzz-unit-file/oss-fuzz-6885
+        fuzz-unit-file/oss-fuzz-6886
 '''.split()