@@ -33,10 +33,11 @@
 #import "OFURLHandler.h"
 #import "OFXMLElement.h"
 
 #import "OFInvalidArgumentException.h"
 #import "OFInvalidFormatException.h"
+#import "OFNotImplementedException.h"
 #import "OFOutOfMemoryException.h"
 #import "OFOutOfRangeException.h"
 #import "OFTruncatedDataException.h"
 #import "OFUnsupportedProtocolException.h"
 
@@ -603,11 +604,12 @@
 {
 	void *pool;
 	OFXMLElement *element;
 
 	if (_itemSize != 1)
-		@throw [OFInvalidArgumentException exception];
+		@throw [OFNotImplementedException exceptionWithSelector: _cmd
+								 object: self];
 
 	pool = objc_autoreleasePoolPush();
 	element = [OFXMLElement
 	    elementWithName: self.className
 		  namespace: OFSerializationNS
@@ -623,11 +625,12 @@
 - (OFData *)messagePackRepresentation
 {
 	OFMutableData *data;
 
 	if (_itemSize != 1)
-		@throw [OFInvalidArgumentException exception];
+		@throw [OFNotImplementedException exceptionWithSelector: _cmd
+								 object: self];
 
 	if (_count <= UINT8_MAX) {
 		uint8_t type = 0xC4;
 		uint8_t tmp = (uint8_t)_count;