diff --git a/S7.Net/Protocol/Serialization.cs b/S7.Net/Protocol/Serialization.cs
index 8e3c4da..40cb629 100644
--- a/S7.Net/Protocol/Serialization.cs
+++ b/S7.Net/Protocol/Serialization.cs
@@ -16,7 +16,7 @@ namespace S7.Net.Protocol
             if (dataItem.Value is string s)
                 return dataItem.VarType == VarType.StringEx
                     ? StringEx.ToByteArray(s, dataItem.Count)
-                    : Types.String.ToByteArray(s);
+                    : Types.String.ToByteArray(s, dataItem.Count);
 
             return SerializeValue(dataItem.Value);
         }
@@ -56,7 +56,10 @@ namespace S7.Net.Protocol
                 case "Single[]":
                     return Types.Single.ToByteArray((float[])value);
                 case "String":
-                    return Types.String.ToByteArray(value as string);
+                    // Hack: This is backwards compatible with the old code, but functionally it's broken
+                    // if the consumer does not pay attention to string length.
+                    var stringVal = (string) value;
+                    return Types.String.ToByteArray(stringVal, stringVal.Length);
                 default:
                     throw new InvalidVariableTypeException();
             }
diff --git a/S7.Net/Types/String.cs b/S7.Net/Types/String.cs
index d1ca263..aaf3428 100644
--- a/S7.Net/Types/String.cs
+++ b/S7.Net/Types/String.cs
@@ -6,11 +6,21 @@
     public class String
     {
         /// <summary>
-        /// Converts a string to S7 bytes
+        /// Converts a string to <paramref name="reservedLength"/> of bytes, padded with 0-bytes if required.
         /// </summary>
-        public static byte[] ToByteArray(string value)
+        /// <param name="value">The string to write to the PLC.</param>
+        /// <param name="reservedLength">The amount of bytes reserved for the <paramref name="value"/> in the PLC.</param>
+        public static byte[] ToByteArray(string value, int reservedLength)
         {
-            return System.Text.Encoding.ASCII.GetBytes(value);
+            var length = value?.Length;
+            if (length > reservedLength) length = reservedLength;
+            var bytes = new byte[reservedLength];
+
+            if (length == null || length == 0) return bytes;
+
+            System.Text.Encoding.ASCII.GetBytes(value, 0, length.Value, bytes, 0);
+
+            return bytes;
         }
         
         /// <summary>