diff --git a/README.md b/README.md
index 4d19def..404989a 100644
--- a/README.md
+++ b/README.md
@@ -167,6 +167,7 @@ PROGRAM MyProgram
     END_VAR
     VAR
         doc : JsonDocument;
+        docBuffer : ARRAY[0..200] OF CHAR;
         myBoolean : JsonBoolean := (Value := TRUE, Key := 'myBoolean');
         myInt : JsonInt := (Value := 1234, Key := 'myInt');
         myDint : JsonDInt := (Value := DINT#12345678, Key := 'myDint');
@@ -190,6 +191,7 @@ PROGRAM MyProgram
             step := Steps#SerializeDocument2;
         Steps#SerializeDocument2:
             // Serialize the document {"myBoolean": true, "myObject": {"myInt": 1234, "myDint": 12345678}}
+            doc.buffer := REF(docBuffer);
             doc.Serialize(doc.buffer);
             SerializedDocument := Arrays.ToString(arr := doc.buffer);
             step := Steps#ParseDocument2;
diff --git a/docs/JsonDocument.md b/docs/JsonDocument.md
index c152941..56e5af1 100644
--- a/docs/JsonDocument.md
+++ b/docs/JsonDocument.md
@@ -10,7 +10,7 @@ classDiagram
 IJsonContainerElement<|--JsonDocument
 IJsonContainerElement : AddElement(IJsonElement)
 JsonDocument : STRING ToString()
-JsonDocument : BOOL Serialize(ARRAY[*] OF CHAR)
+JsonDocument : BOOL Serialize()
 JsonDocument : IJsonElement GetRootElement()
 JsonDocument : ClearBuffer(BOOL)
 JsonDocument : Reset()
@@ -23,8 +23,8 @@ JsonDocument : Reset()
 
 Returns the JSON string of the JSON document (max. 254 characters)
 
-### Serialize(IN_OUT buf : ARRAY[*] OF CHAR) : BOOL
-Serializes the JSON document ino a ARRAY OF CHAR
+### Serialize() : BOOL
+Serializes the JSON document ino a ARRAY OF CHAR. JsonDocument.buffer must be set before.
 
 ### GetRootElement() : IJsonElement
 Returns root element of the JSON document
@@ -33,7 +33,7 @@ Returns root element of the JSON document
 Add a new element to the JSON document
 
 ### ClearBuffer(hard : BOOL)
-Clear the buffer logically (fast). If `hard = TRUE` then delete the buffer also physically (slow)
+Clear the buffer logically (fast). If `hard = TRUE` then delete the buffer also physically (slow) JsonDocument.buffer must be set before.
 
 ### Reset()
 Reset the complete object tree and the destination buffer of the JSON document for the purpose, a new JSON object should be created.