diff --git a/index.ts b/index.ts
index 0425d35..b43227d 100644
--- a/index.ts
+++ b/index.ts
@@ -1248,11 +1248,11 @@ export class RFC5424 extends RFC {
           if (this.timestampTZ) {
             timestamp = moment(options.timestamp)
               .utc()
-              .format('YYYY-MM-DDThh:mm:ss.SSSSSSZ');
+              .format('YYYY-MM-DDThh:mm:ss.SSSZ');
           } else {
             timestamp = moment(options.timestamp)
               .utc()
-              .format('YYYY-MM-DDThh:mm:ss.SSSSSS');
+              .format('YYYY-MM-DDThh:mm:ss.SSS');
           }
         } else {
           if (this.timestampTZ) {
@@ -1272,7 +1272,7 @@ export class RFC5424 extends RFC {
             timeQuality += ' isSynced=1';
             timeQuality += ' syncAccuracy=0';
             timestamp = moment(options.timestamp)
-              .format('YYYY-MM-DDThh:mm:ss.SSSSSSZ');
+              .format('YYYY-MM-DDThh:mm:ss.SSSZ');
           } else {
             timestamp = moment(options.timestamp)
               .format('YYYY-MM-DDThh:mm:ssZ');
@@ -1283,7 +1283,7 @@ export class RFC5424 extends RFC {
             timeQuality += ' isSynced=1';
             timeQuality += ' syncAccuracy=0';
             timestamp = moment(options.timestamp)
-              .format('YYYY-MM-DDThh:mm:ss.SSSSSS');
+              .format('YYYY-MM-DDThh:mm:ss.SSS');
           } else {
             timestamp = moment(options.timestamp).format('YYYY-MM-DDThh:mm:ss');
           }
diff --git a/tests/syslog.test.js b/tests/syslog.test.js
index c0af3ee..54c84bc 100644
--- a/tests/syslog.test.js
+++ b/tests/syslog.test.js
@@ -343,7 +343,7 @@ describe('RFC5424 Class Tests', () => {
         '[ourSDID@32473 test=test]'
       ]
     });
-    resultMsg = /<190>1 \d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}.\d{6} /;
+    resultMsg = /<190>1 \d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}.\d{1,3} /;
     expect(result).toMatch(resultMsg);
     rfc5424 = new SyslogPro.RFC5424({
       timestamp: true,
@@ -352,7 +352,7 @@ describe('RFC5424 Class Tests', () => {
       timestampMS: true,
     });
     result = rfc5424.buildMessage('hello');
-    resultMsg = /<190>1 \d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}.\d{6}\+/;
+    resultMsg = /<190>1 \d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}.\d{1,3}\+/;
     expect(result).toMatch(resultMsg);
     rfc5424 = new SyslogPro.RFC5424({
       timestamp: true,
@@ -379,7 +379,7 @@ describe('RFC5424 Class Tests', () => {
       timestampMS: true,
     });
     result = rfc5424.buildMessage('hello');
-    resultMsg = /<190>1 \d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}.\d{6} /;
+    resultMsg = /<190>1 \d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}.\d{1,3} /;
     expect(result).toMatch(resultMsg);
     rfc5424 = new SyslogPro.RFC5424({
       timestamp: true,
@@ -388,7 +388,7 @@ describe('RFC5424 Class Tests', () => {
       timestampMS: true,
     });
     result = rfc5424.buildMessage('hello');
-    resultMsg = /<190>1 \d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}.\d{6}\+/;
+    resultMsg = /<190>1 \d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}.\d{1,3}\+/;
     expect(result).toMatch(resultMsg);
     rfc5424 = new SyslogPro.RFC5424({
       timestamp: true,
@@ -409,7 +409,7 @@ describe('RFC5424 Class Tests', () => {
     });
     const timestamp = new Date('2020-01-01T01:23:45.678Z');
     const result = rfc5424.buildMessage('hello', { timestamp });
-    expect(result.startsWith('<190>1 2020-01-01T01:23:45.678000+00:00 ')).toBe(true);
+    expect(result.startsWith('<190>1 2020-01-01T01:23:45.678+00:00 ')).toBe(true);
   });
   test('RFC5424 BuildMessage with hostname and applicationName options', () => {
     const rfc5424 = new SyslogPro.RFC5424();