Index: src/OFXMLElement.m
==================================================================
--- src/OFXMLElement.m
+++ src/OFXMLElement.m
@@ -239,23 +239,20 @@
 			[all_namespaces setObject: obj
 					   forKey: key];
 	} else
 		all_namespaces = namespaces;
 
+	prefix = [all_namespaces objectForKey: (ns != nil ? ns : @"")];
+
 	i = 0;
 	len = [name cStringLength] + 3;
 	str_c = [self allocMemoryWithSize: len];
 
 	/* Start of tag */
 	str_c[i++] = '<';
 
-	if ((ns == nil && def_ns != nil) || (ns != nil && def_ns == nil) ||
-	    (ns != nil && ![ns isEqual: def_ns])) {
-		if ((prefix = [all_namespaces objectForKey:
-		    (ns != nil ? ns : (OFString*)@"")]) == nil)
-			@throw [OFUnboundNamespaceException newWithClass: isa
-							       namespace: ns];
+	if (prefix != nil && ![ns isEqual: def_ns]) {
 		len += [prefix cStringLength] + 1;
 		@try {
 			str_c = [self resizeMemory: str_c
 					    toSize: len];
 		} @catch (id e) {
@@ -269,10 +266,31 @@
 		str_c[i++] = ':';
 	}
 
 	memcpy(str_c + i, [name cString], [name cStringLength]);
 	i += [name cStringLength];
+
+	/* xmlns if necessary */
+	if (ns != nil && prefix == nil && ![ns isEqual: def_ns]) {
+		len += [ns cStringLength] + 9;
+
+		@try {
+			str_c = [self resizeMemory: str_c
+					    toSize: len];
+		} @catch (id e) {
+			[self freeMemory: str_c];
+			@throw e;
+		}
+
+		memcpy(str_c + i, " xmlns='", 8);
+		i += 8;
+		memcpy(str_c + i, [ns cString], [ns cStringLength]);
+		i += [ns cStringLength];
+		str_c[i++] = '\'';
+
+		def_ns = ns;
+	}
 
 	/* Attributes */
 	attrs_carray = [attributes cArray];
 	attrs_count = [attributes count];
 
@@ -333,11 +351,11 @@
 		for (j = 0; j < children_count; j++)
 			append(tmp, @selector(
 			    appendCStringWithoutUTF8Checking:),
 			    [[children_carray[j]
 			    _stringValueWithParentNamespaces: all_namespaces
-			    parentDefaultNamespace: defaultNamespace] cString]);
+			    parentDefaultNamespace: def_ns] cString]);
 
 		len += [tmp cStringLength] + [name cStringLength] + 2;
 		@try {
 			str_c = [self resizeMemory: str_c
 					    toSize: len];

Index: tests/OFXMLElementTests.m
==================================================================
--- tests/OFXMLElementTests.m
+++ tests/OFXMLElementTests.m
@@ -46,11 +46,17 @@
 					   namespace: @"urn:objfw:test"]) &&
 	    R([elem[2] addAttributeWithName: @"test"
 				stringValue: @"test"]) &&
 	    R([elem[2] setPrefix: @"objfw-test"
 		    forNamespace: @"urn:objfw:test"]) &&
-	    [[elem[2] stringValue] isEqual: @"<objfw-test:foo test='test'/>"])
+	    [[elem[2] stringValue] isEqual: @"<objfw-test:foo test='test'/>"] &&
+	    (elem[3] = [OFXMLElement elementWithName: @"foo"
+					   namespace: @"urn:objfw:test"]) &&
+	    R([elem[3] addAttributeWithName: @"test"
+				stringValue: @"test"]) &&
+	    [[elem[3] stringValue] isEqual:
+	    @"<foo xmlns='urn:objfw:test' test='test'/>"])
 
 	TEST(@"+[elementWithName:namespace:stringValue:]",
 	    (elem[3] = [OFXMLElement elementWithName: @"foo"
 					   namespace: @"urn:objfw:test"
 					 stringValue: @"x"]) &&