diff --git a/source/common/router/header_formatter.cc b/source/common/router/header_formatter.cc
index b76fd90f5bbe2..d171b82d25c76 100644
--- a/source/common/router/header_formatter.cc
+++ b/source/common/router/header_formatter.cc
@@ -11,6 +11,7 @@
 #include "common/json/json_loader.h"
 #include "common/request_info/utility.h"
 
+#include "absl/strings/str_cat.h"
 #include "absl/types/optional.h"
 
 namespace Envoy {
@@ -143,9 +144,13 @@ RequestInfoHeaderFormatter::RequestInfoHeaderFormatter(absl::string_view field_n
     }
     field_extractor_ = [this, pattern](const Envoy::RequestInfo::RequestInfo& request_info) {
       const auto& formatters = start_time_formatters_.at(pattern);
-      ASSERT(formatters.size() == 1);
       Http::HeaderMapImpl empty_map;
-      return formatters.at(0)->format(empty_map, empty_map, empty_map, request_info);
+      std::string formatted;
+      for (const auto& formatter : formatters) {
+        absl::StrAppend(&formatted,
+                        formatter->format(empty_map, empty_map, empty_map, request_info));
+      }
+      return formatted;
     };
   } else if (field_name.find("UPSTREAM_METADATA") == 0) {
     field_extractor_ =
diff --git a/test/common/router/header_formatter_test.cc b/test/common/router/header_formatter_test.cc
index 000549573560e..ceaad6c6b4835 100644
--- a/test/common/router/header_formatter_test.cc
+++ b/test/common/router/header_formatter_test.cc
@@ -617,6 +617,10 @@ match: { prefix: "/new_endpoint" }
         key: "x-request-start"
         value: "%START_TIME(%s.%3f)%"
       append: true
+    - header:
+        key: "x-request-start-multiple"
+        value: "%START_TIME(%s.%3f)% %START_TIME% %START_TIME(%s)%"
+      append: true
     - header:
         key: "x-request-start-f"
         value: "%START_TIME(f)%"
@@ -640,14 +644,17 @@ match: { prefix: "/new_endpoint" }
 
   // Initialize start_time as 2018-04-03T23:06:09.123Z in microseconds.
   const SystemTime start_time(std::chrono::microseconds(1522796769123456));
-  EXPECT_CALL(request_info, startTime()).Times(4).WillRepeatedly(Return(start_time));
+  EXPECT_CALL(request_info, startTime()).Times(7).WillRepeatedly(Return(start_time));
 
   resp_header_parser->evaluateHeaders(headerMap, request_info);
   EXPECT_TRUE(headerMap.has("x-client-ip"));
+  EXPECT_TRUE(headerMap.has("x-request-start-multiple"));
   EXPECT_TRUE(headerMap.has("x-safe"));
   EXPECT_FALSE(headerMap.has("x-nope"));
   EXPECT_TRUE(headerMap.has("x-request-start"));
   EXPECT_EQ("1522796769.123", headerMap.get_("x-request-start"));
+  EXPECT_EQ("1522796769.123 2018-04-03T23:06:09.123Z 1522796769",
+            headerMap.get_("x-request-start-multiple"));
   EXPECT_TRUE(headerMap.has("x-request-start-f"));
   EXPECT_EQ("f", headerMap.get_("x-request-start-f"));
   EXPECT_TRUE(headerMap.has("x-request-start-default"));
diff --git a/test/common/router/header_parser_corpus/clusterfuzz-testcase-header_parser_fuzz_test-6195059702628352 b/test/common/router/header_parser_corpus/clusterfuzz-testcase-header_parser_fuzz_test-6195059702628352
new file mode 100644
index 0000000000000..b1d85a401670a
--- /dev/null
+++ b/test/common/router/header_parser_corpus/clusterfuzz-testcase-header_parser_fuzz_test-6195059702628352
@@ -0,0 +1,8 @@
+headers_to_add {
+  header {
+    value: "%START_TIMEY()%T      %START_TIME(f, %�{{{{{_�����������85request_i:	1�227 f55555_n555555555555%85nfo 5#555.55f, %1f,  %85/5_inf %8,,,,,,,,,,,,,,,,,,,,,,,,,55555 start_timefo 5#5555#555.55f, %1f,  %85/55ime:	15227 f %1f,  %8555555555  %85/5555Fme:	15227 f-5555_inf 965L5559f)%"
+  }
+}
+request_info {
+  start_time:	1522796769123
+}