Index: src/OFXMLAttribute.h
==================================================================
--- src/OFXMLAttribute.h
+++ src/OFXMLAttribute.h
@@ -26,11 +26,13 @@
  *
  * @brief A representation of an attribute of an XML element as an object.
  */
 @interface OFXMLAttribute: OFXMLNode
 {
+#if defined(OF_XML_ELEMENT_M) || defined(OF_XML_PARSER_M)
 @public
+#endif
 	OFString *_name, *_Nullable _namespace, *_stringValue;
 }
 
 /*!
  * @brief The name of the attribute.

Index: src/OFXMLElement.m
==================================================================
--- src/OFXMLElement.m
+++ src/OFXMLElement.m
@@ -15,10 +15,12 @@
  * file.
  */
 
 #include "config.h"
 
+#define OF_XML_ELEMENT_M
+
 #include <stdlib.h>
 #include <string.h>
 
 #include <assert.h>
 
@@ -189,11 +191,12 @@
 - (instancetype)initWithElement: (OFXMLElement *)element
 {
 	self = [super of_init];
 
 	@try {
-		if (element == nil)
+		if (element == nil ||
+		    ![element isKindOfClass: [OFXMLElement class]])
 			@throw [OFInvalidArgumentException exception];
 
 		_name = [element->_name copy];
 		_namespace = [element->_namespace copy];
 		_defaultNamespace = [element->_defaultNamespace copy];
@@ -758,10 +761,13 @@
 	return [element autorelease];
 }
 
 - (void)addAttribute: (OFXMLAttribute *)attribute
 {
+	if (![attribute isKindOfClass: [OFXMLAttribute class]])
+		@throw [OFInvalidArgumentException exception];
+
 	if (_attributes == nil)
 		_attributes = [[OFMutableArray alloc] init];
 
 	if ([self attributeForName: attribute->_name
 			 namespace: attribute->_namespace] == nil)

Index: src/OFXMLParser.m
==================================================================
--- src/OFXMLParser.m
+++ src/OFXMLParser.m
@@ -14,10 +14,12 @@
  * LICENSE.GPLv2 or LICENSE.GPLv3 respectively included in the packaging of this
  * file.
  */
 
 #include "config.h"
+
+#define OF_XML_PARSER_M
 
 #include <string.h>
 
 #import "OFXMLParser.h"
 #import "OFString.h"