diff --git a/S7.Net/Plc.Clock.cs b/S7.Net/Plc.Clock.cs
index 82394ce..45ccb36 100644
--- a/S7.Net/Plc.Clock.cs
+++ b/S7.Net/Plc.Clock.cs
@@ -11,6 +11,10 @@ partial class Plc
 {
     private const byte SzlFunctionGroupTimers = 0x07;
     private const byte SzlSubFunctionReadClock = 0x01;
+    private const byte SzlSubFunctionWriteClock = 0x02;
+    private const byte TransportSizeOctetString = 0x09;
+    private const int PduErrOffset = 20;
+    private const int UserDataResultOffset = PduErrOffset + 2;
 
     private static byte[] BuildClockReadRequest()
     {
@@ -25,29 +29,55 @@ partial class Plc
 
     private static DateTime ParseClockReadResponse(byte[] message)
     {
-        const int pduErrOffset = 20;
-        const int dtResultOffset = pduErrOffset + 2;
-        const int dtLenOffset = dtResultOffset + 2;
-        const int dtValueOffset = dtLenOffset + 4;
+        const int udLenOffset = UserDataResultOffset + 2;
+        const int udValueOffset = udLenOffset + 4;
 
-        var pduErr = Word.FromByteArray(message.Skip(pduErrOffset).Take(2).ToArray());
-        if (pduErr != 0)
-        {
-            throw new Exception($"Response from PLC indicates error 0x{pduErr:X4}.");
-        }
+        AssertPduResult(message);
+        AssertUserDataResult(message, 0xff);
 
-        var dtResult = message[dtResultOffset];
-        if (dtResult != 0xff)
-        {
-            throw new Exception($"Response from PLC indicates error 0x{dtResult:X2}.");
-        }
-
-        var len = Word.FromByteArray(message.Skip(dtLenOffset).Take(2).ToArray());
+        var len = Word.FromByteArray(message.Skip(udLenOffset).Take(2).ToArray());
         if (len != Types.DateTime.Length)
         {
             throw new Exception($"Unexpected response length {len}, expected {Types.DateTime.Length}.");
         }
 
-        return Types.DateTime.FromByteArray(message.Skip(dtValueOffset).Take(Types.DateTime.Length).ToArray());
+        return Types.DateTime.FromByteArray(message.Skip(udValueOffset).Take(Types.DateTime.Length).ToArray());
+    }
+
+    private static byte[] BuildClockWriteRequest(DateTime value)
+    {
+        var stream = new MemoryStream();
+
+        WriteUserDataRequest(stream, SzlFunctionGroupTimers, SzlSubFunctionWriteClock, 14);
+        stream.Write(new byte[] { 0xff, TransportSizeOctetString, 0x00, Types.DateTime.Length });
+        stream.Write(new byte[] { 0x00, 0x19 }); // Start of actual DateTime value, DateTime.ToByteArray is broken
+        stream.Write(Types.DateTime.ToByteArray(value));
+
+        stream.SetLength(stream.Position);
+        return stream.ToArray();
+    }
+
+    private static void ParseClockWriteResponse(byte[] message)
+    {
+        AssertPduResult(message);
+        AssertUserDataResult(message, 0x0a);
+    }
+
+    private static void AssertPduResult(byte[] message)
+    {
+        var pduErr = Word.FromByteArray(message.Skip(PduErrOffset).Take(2).ToArray());
+        if (pduErr != 0)
+        {
+            throw new Exception($"Response from PLC indicates error 0x{pduErr:X4}.");
+        }
+    }
+
+    private static void AssertUserDataResult(byte[] message, byte expected)
+    {
+        var dtResult = message[UserDataResultOffset];
+        if (dtResult != expected)
+        {
+            throw new Exception($"Response from PLC was 0x{dtResult:X2}, expected 0x{expected:X2}.");
+        }
     }
 }
\ No newline at end of file
diff --git a/S7.Net/PlcAsynchronous.cs b/S7.Net/PlcAsynchronous.cs
index 7a1dd44..8b828f3 100644
--- a/S7.Net/PlcAsynchronous.cs
+++ b/S7.Net/PlcAsynchronous.cs
@@ -335,7 +335,10 @@ namespace S7.Net
         /// <returns>A task that represents the asynchronous operation.</returns>
         public async Task WriteClockAsync(System.DateTime value, CancellationToken cancellationToken = default)
         {
-            throw new NotImplementedException();
+            var request = BuildClockWriteRequest(value);
+            var response = await RequestTsduAsync(request, cancellationToken);
+
+            ParseClockWriteResponse(response);
         }
 
         /// <summary>
diff --git a/S7.Net/PlcSynchronous.cs b/S7.Net/PlcSynchronous.cs
index cfb4d99..2e28131 100644
--- a/S7.Net/PlcSynchronous.cs
+++ b/S7.Net/PlcSynchronous.cs
@@ -510,7 +510,10 @@ namespace S7.Net
         /// <param name="value">The date and time to set the PLC clock to.</param>
         public void WriteClock(System.DateTime value)
         {
-            throw new NotImplementedException();
+            var request = BuildClockWriteRequest(value);
+            var response = RequestTsdu(request);
+
+            ParseClockWriteResponse(response);
         }
 
         /// <summary>