diff --git a/pmml-rexp/src/main/java/org/jpmml/rexp/BinaryTreeConverter.java b/pmml-rexp/src/main/java/org/jpmml/rexp/BinaryTreeConverter.java
index 3a46a09..fe070fb 100644
--- a/pmml-rexp/src/main/java/org/jpmml/rexp/BinaryTreeConverter.java
+++ b/pmml-rexp/src/main/java/org/jpmml/rexp/BinaryTreeConverter.java
@@ -115,7 +115,7 @@ private void encodeResponse(S4Object responses, RExpEncoder encoder){
 
 			RExp targetVariable = variables.getElement(variableName);
 
-			RStringVector targetVariableClass = RExpUtil.getClassNames(targetVariable);
+			RStringVector targetVariableClass = targetVariable._class();
 
 			RStringVector targetCategories = levels.getStringElement(variableName);
 
diff --git a/pmml-rexp/src/main/java/org/jpmml/rexp/ConverterFactory.java b/pmml-rexp/src/main/java/org/jpmml/rexp/ConverterFactory.java
index 1582885..c82424b 100644
--- a/pmml-rexp/src/main/java/org/jpmml/rexp/ConverterFactory.java
+++ b/pmml-rexp/src/main/java/org/jpmml/rexp/ConverterFactory.java
@@ -37,7 +37,7 @@ protected ConverterFactory(){
 	}
 
 	public <R extends RExp> Converter<R> newConverter(R rexp){
-		RStringVector classNames = RExpUtil.getClassNames(rexp);
+		RStringVector classNames = rexp._class();
 
 		for(String className : classNames){
 			Class<? extends Converter<?>> clazz = ConverterFactory.converters.get(className);
diff --git a/pmml-rexp/src/main/java/org/jpmml/rexp/DecorationUtil.java b/pmml-rexp/src/main/java/org/jpmml/rexp/DecorationUtil.java
index 653391f..b322586 100644
--- a/pmml-rexp/src/main/java/org/jpmml/rexp/DecorationUtil.java
+++ b/pmml-rexp/src/main/java/org/jpmml/rexp/DecorationUtil.java
@@ -65,7 +65,7 @@ public RVector<?> getVectorElement(RGenericVector model, String name){
 
 	static
 	private RuntimeException toDecorationException(RGenericVector model, String name, Exception e){
-		RStringVector classNames = RExpUtil.getClassNames(model);
+		RStringVector classNames = model._class();
 
 		String className = classNames.getValue(0);
 
diff --git a/pmml-rexp/src/main/java/org/jpmml/rexp/RExp.java b/pmml-rexp/src/main/java/org/jpmml/rexp/RExp.java
index eeb011a..46bcf88 100644
--- a/pmml-rexp/src/main/java/org/jpmml/rexp/RExp.java
+++ b/pmml-rexp/src/main/java/org/jpmml/rexp/RExp.java
@@ -35,6 +35,10 @@ public void write(RDataOutput output) throws IOException {
 		throw new UnsupportedOperationException();
 	}
 
+	public RStringVector _class(){
+		return getStringAttribute("class");
+	}
+
 	public RStringVector names(){
 		return getStringAttribute("names");
 	}
diff --git a/pmml-rexp/src/main/java/org/jpmml/rexp/RExpUtil.java b/pmml-rexp/src/main/java/org/jpmml/rexp/RExpUtil.java
index 11d3649..e1a10f5 100644
--- a/pmml-rexp/src/main/java/org/jpmml/rexp/RExpUtil.java
+++ b/pmml-rexp/src/main/java/org/jpmml/rexp/RExpUtil.java
@@ -65,13 +65,6 @@ public String getVectorType(Class<?> clazz){
 		return vectorType;
 	}
 
-	static
-	public RStringVector getClassNames(RExp rexp){
-		RStringVector result = rexp.getStringAttribute("class");
-
-		return result;
-	}
-
 	static
 	public String makeName(String string){
 		StringBuilder sb = new StringBuilder();
diff --git a/pmml-rexp/src/test/java/org/jpmml/rexp/SerializeTest.java b/pmml-rexp/src/test/java/org/jpmml/rexp/SerializeTest.java
index eb8c6e6..3bf3d9b 100644
--- a/pmml-rexp/src/test/java/org/jpmml/rexp/SerializeTest.java
+++ b/pmml-rexp/src/test/java/org/jpmml/rexp/SerializeTest.java
@@ -129,7 +129,7 @@ private void checkDataFrame(RGenericVector dataFrame){
 		assertTrue(dataFrame.hasAttribute("names"));
 		assertTrue(dataFrame.hasAttribute("row.names"));
 
-		assertEquals(Arrays.asList("data.frame"), (dataFrame.getStringAttribute("class")).getValues());
+		assertEquals(Arrays.asList("data.frame"), (dataFrame._class()).getValues());
 
 		assertEquals(5, dataFrame.size());