Index: src/OFMutableString.m
==================================================================
--- src/OFMutableString.m
+++ src/OFMutableString.m
@@ -39,10 +39,13 @@
 		[self freeMemory: string];
 
 	len = strlen(str);
 
 	switch (of_string_check_utf8(str, len)) {
+	case 0:
+		is_utf8 = NO;
+		break;
 	case 1:
 		is_utf8 = YES;
 		break;
 	case -1:
 		string = NULL;
@@ -132,11 +135,16 @@
 	return self;
 }
 
 - appendString: (OFString*)str
 {
-	return [self appendCStringWithoutUTF8Checking: [str cString]];
+	[self appendCStringWithoutUTF8Checking: [str cString]];
+
+	if (str->is_utf8)
+		is_utf8 = YES;
+
+	return self;
 }
 
 - appendWithFormat: (OFString*)fmt, ...
 {
 	id ret;

Index: src/OFString.m
==================================================================
--- src/OFString.m
+++ src/OFString.m
@@ -457,14 +457,33 @@
 	return self;
 }
 
 - initWithString: (OFString*)str
 {
+	Class c;
+
 	self = [super init];
 
-	string = strdup([str cString]);
+	string = (char*)[str cString];
 	length = [str cStringLength];
+
+	switch (of_string_check_utf8(string, length)) {
+		case 1:
+			is_utf8 = YES;
+			break;
+		case -1:
+			c = isa;
+			[self dealloc];
+			@throw [OFInvalidEncodingException newWithClass: c];
+	}
+
+	if ((string = strdup(string)) == NULL) {
+		c = isa;
+		[self dealloc];
+		@throw [OFOutOfMemoryException newWithClass: c
+						       size: length + 1];
+	}
 
 	@try {
 		[self addMemoryToPool: string];
 	} @catch (OFException *e) {
 		/*

Index: src/OFXMLParser.m
==================================================================
--- src/OFXMLParser.m
+++ src/OFXMLParser.m
@@ -510,10 +510,11 @@
 	OFString *ret;
 
 	last = 0;
 	in_entity = NO;
 	ret = [OFMutableString string];
+	ret->is_utf8 = is_utf8;
 
 	for (i = 0; i < length; i++) {
 		if (!in_entity && string[i] == '&') {
 			[ret appendCStringWithoutUTF8Checking: string + last
 						    length: i - last];
@@ -523,19 +524,24 @@
 		} else if (in_entity && string[i] == ';') {
 			char *entity = string + last;
 			size_t len = i - last;
 
 			if (len == 2 && !memcmp(entity, "lt", 2))
-				[ret appendString: @"<"];
+				[ret appendCStringWithoutUTF8Checking: "<"
+							       length: 1];
 			else if (len == 2 && !memcmp(entity, "gt", 2))
-				[ret appendString: @">"];
+				[ret appendCStringWithoutUTF8Checking: ">"
+							       length: 1];
 			else if (len == 4 && !memcmp(entity, "quot", 4))
-				[ret appendString: @"\""];
+				[ret appendCStringWithoutUTF8Checking: "\""
+							       length: 1];
 			else if (len == 4 && !memcmp(entity, "apos", 4))
-				[ret appendString: @"'"];
+				[ret appendCStringWithoutUTF8Checking: "'"
+							       length: 1];
 			else if (len == 3 && !memcmp(entity, "amp", 3))
-				[ret appendString: @"&"];
+				[ret appendCStringWithoutUTF8Checking: "&"
+							       length: 1];
 			else if (entity[0] == '#') {
 				OFAutoreleasePool *pool;
 				OFString *tmp;
 
 				pool = [[OFAutoreleasePool alloc] init];