diff --git a/FuzzTesting/FailCases/clusterfuzz-testcase-minimized-FuzzJSON_debug-6286338012282880 b/FuzzTesting/FailCases/clusterfuzz-testcase-minimized-FuzzJSON_debug-6286338012282880
new file mode 100644
index 000000000..064746ff3
--- /dev/null
+++ b/FuzzTesting/FailCases/clusterfuzz-testcase-minimized-FuzzJSON_debug-6286338012282880
@@ -0,0 +1 @@
+{"wktTimestamp":"9999-12-31T23:59:60Z"}
\ No newline at end of file
diff --git a/Sources/SwiftProtobuf/Google_Protobuf_Timestamp+Extensions.swift b/Sources/SwiftProtobuf/Google_Protobuf_Timestamp+Extensions.swift
index ab0a68b87..cad7355f2 100644
--- a/Sources/SwiftProtobuf/Google_Protobuf_Timestamp+Extensions.swift
+++ b/Sources/SwiftProtobuf/Google_Protobuf_Timestamp+Extensions.swift
@@ -167,9 +167,6 @@ private func parseTimestamp(s: String) throws -> (Int64, Int32) {
       adjusted += Int64(hourOffset) * Int64(3600)
       adjusted += Int64(minuteOffset) * Int64(60)
     }
-    if adjusted < minTimestampSeconds || adjusted > maxTimestampSeconds {
-      throw JSONDecodingError.malformedTimestamp
-    }
     seconds = adjusted
     pos += 6
   } else if value[pos] == letterZ { // "Z" indicator for UTC
@@ -181,6 +178,9 @@ private func parseTimestamp(s: String) throws -> (Int64, Int32) {
   if pos != value.count {
     throw JSONDecodingError.malformedTimestamp
   }
+  guard seconds >= minTimestampSeconds && seconds <= maxTimestampSeconds else {
+    throw JSONDecodingError.malformedTimestamp
+  }
   return (seconds, nanos)
 }
 
diff --git a/Tests/SwiftProtobufTests/Test_FuzzTests.swift b/Tests/SwiftProtobufTests/Test_FuzzTests.swift
index 23ffd0f1b..463c7a056 100644
--- a/Tests/SwiftProtobufTests/Test_FuzzTests.swift
+++ b/Tests/SwiftProtobufTests/Test_FuzzTests.swift
@@ -121,6 +121,9 @@ final class Test_FuzzTests: XCTestCase {
     // This actually fails when the fuzzer was trying to write it back out again.
     let msg = try! SwiftProtoTesting_Fuzz_Message(jsonString: "   {\"wktAny\":  {}}  ")
     XCTAssertEqual(try! msg.jsonString(), "{\"wktAny\":{}}")
+
+    // FailCases/clusterfuzz-testcase-minimized-FuzzJSON_debug-6286338012282880
+    assertJSONFails("{\"wktTimestamp\":\"9999-12-31T23:59:60Z\"}")
   }
 
   func test_TextFormat() {