Index: src/OFDate.m
==================================================================
--- src/OFDate.m
+++ src/OFDate.m
@@ -31,10 +31,11 @@
 # import "OFMutex.h"
 #endif
 #import "OFStrPTime.h"
 #import "OFString.h"
 #import "OFSystemInfo.h"
+#import "OFXMLAttribute.h"
 #import "OFXMLElement.h"
 
 #import "OFInitializationFailedException.h"
 #import "OFInvalidArgumentException.h"
 #import "OFInvalidFormatException.h"
@@ -504,10 +505,14 @@
 		unsigned long long value;
 
 		if (![element.name isEqual: @"OFDate"] ||
 		    ![element.namespace isEqual: OFSerializationNS])
 			@throw [OFInvalidArgumentException exception];
+
+		if (![[element attributeForName: @"encoding"].stringValue
+		    isEqual: @"hex"])
+			@throw [OFInvalidFormatException exception];
 
 		value = [element unsignedLongLongValueWithBase: 16];
 
 		if (value > UINT64_MAX)
 			@throw [OFOutOfRangeException exception];
@@ -588,10 +593,11 @@
 	OFXMLElement *element;
 
 	element = [OFXMLElement elementWithName: @"OFDate"
 				      namespace: OFSerializationNS];
 
+	[element addAttributeWithName: @"encoding" stringValue: @"hex"];
 	element.stringValue = [OFString stringWithFormat: @"%016" PRIx64,
 	    OFFromBigEndian64(OFDoubleToRawUInt64(OFToBigEndianDouble(
 	    self.timeIntervalSince1970)))];
 
 	[element retain];

Index: tests/serialization.xml
==================================================================
--- tests/serialization.xml
+++ tests/serialization.xml
@@ -55,13 +55,13 @@
         <OFString>Qu&quot;xbar
 test</OFString>
         <OFNumber type='signed'>1234</OFNumber>
         <OFNumber type='float'>40934a456d5cfaad</OFNumber>
         <OFMutableString>asd</OFMutableString>
-        <OFDate>40934a456d5cfaad</OFDate>
+        <OFDate encoding='hex'>40934a456d5cfaad</OFDate>
       </OFArray>
     </key>
     <object>
       <OFString>Hello</OFString>
     </object>
   </OFMutableDictionary>
 </serialization>