diff --git a/test/common/access_log/access_log_formatter_corpus/clusterfuzz-testcase-minimized-access_log_formatter_fuzz_test-5701824317751296 b/test/common/access_log/access_log_formatter_corpus/clusterfuzz-testcase-minimized-access_log_formatter_fuzz_test-5701824317751296
new file mode 100644
index 000000000000..542c0daf722b
--- /dev/null
+++ b/test/common/access_log/access_log_formatter_corpus/clusterfuzz-testcase-minimized-access_log_formatter_fuzz_test-5701824317751296
@@ -0,0 +1 @@
+format: "%START_TIME(%f)%" request_info {   start_time: 18446744073709551615 } 
diff --git a/test/common/router/header_parser_corpus/clusterfuzz-testcase-minimized-header_parser_fuzz_test-5647641023610880 b/test/common/router/header_parser_corpus/clusterfuzz-testcase-minimized-header_parser_fuzz_test-5647641023610880
new file mode 100644
index 000000000000..1251ede979a5
--- /dev/null
+++ b/test/common/router/header_parser_corpus/clusterfuzz-testcase-minimized-header_parser_fuzz_test-5647641023610880
@@ -0,0 +1 @@
+headers_to_add {   header {     key: " "     value: "%START_TIME(ÿ)%"   } } request_info {   start_time: 9799832698963886077 } 
diff --git a/test/fuzz/utility.h b/test/fuzz/utility.h
index 6933b2313420..3c5fdf1158db 100644
--- a/test/fuzz/utility.h
+++ b/test/fuzz/utility.h
@@ -37,8 +37,11 @@ inline TestRequestInfo fromRequestInfo(const test::fuzz::RequestInfo& request_in
   TestRequestInfo test_request_info;
   test_request_info.metadata_ = request_info.dynamic_metadata();
   // libc++ clocks don't track at nanosecond on OS X.
-  test_request_info.start_time_ =
-      SystemTime(std::chrono::microseconds(request_info.start_time() / 1000));
+  const auto start_time =
+      std::numeric_limits<std::chrono::nanoseconds::rep>::max() < request_info.start_time()
+          ? 0
+          : request_info.start_time() / 1000;
+  test_request_info.start_time_ = SystemTime(std::chrono::microseconds(start_time));
   if (request_info.has_response_code()) {
     test_request_info.response_code_ = request_info.response_code().value();
   }