diff --git a/examples/12-example-byte-manipulation.yaml b/examples/12-example-byte-manipulation.yaml
index 9973b6fa..7bad4b34 100644
--- a/examples/12-example-byte-manipulation.yaml
+++ b/examples/12-example-byte-manipulation.yaml
@@ -30,7 +30,7 @@ functions:
     code: |
       global newSchemaId
       log.info("Replacing schema in message value: {}", value)
-      if value is not None:
+      if isinstance(value, list):
         if value[0] == 0 and len(value) >= 5:
           value[1] = (newSchemaId & 0xff000000) >> 24
           value[2] = (newSchemaId & 0xff0000) >> 16
diff --git a/ksml/src/main/java/io/axual/ksml/python/PythonDataObjectMapper.java b/ksml/src/main/java/io/axual/ksml/python/PythonDataObjectMapper.java
index fca42e17..6fd5c830 100644
--- a/ksml/src/main/java/io/axual/ksml/python/PythonDataObjectMapper.java
+++ b/ksml/src/main/java/io/axual/ksml/python/PythonDataObjectMapper.java
@@ -28,6 +28,7 @@
 import io.axual.ksml.util.ExecutionUtil;
 import org.graalvm.polyglot.Value;
 
+import java.util.ArrayList;
 import java.util.Map;
 
 public class PythonDataObjectMapper extends NativeDataObjectMapper {
@@ -146,7 +147,13 @@ public Value fromDataObject(DataObject object) {
         if (object instanceof DataLong val) return Value.asValue(val.value());
         if (object instanceof DataFloat val) return Value.asValue(val.value());
         if (object instanceof DataDouble val) return Value.asValue(val.value());
-        if (object instanceof DataBytes val) return Value.asValue(val.value());
+        if (object instanceof DataBytes val) {
+            // Convert the contained byte array to a list, so it can be converted to a Python list by the PythonFunction
+            // wrapper code downstream...
+            final var bytes = new ArrayList<Byte>(val.value().length);
+            for (byte b : val.value()) bytes.add(b);
+            return Value.asValue(bytes);
+        }
         if (object instanceof DataString val) return Value.asValue(val.value());
         if (object instanceof DataList val) return Value.asValue(fromDataList(val));
         if (object instanceof DataStruct val) return Value.asValue(fromDataStruct(val));