Index: src/OFMutableString.m
==================================================================
--- src/OFMutableString.m
+++ src/OFMutableString.m
@@ -132,17 +132,22 @@
 	length = newLength;
 }
 
 - (void)setToCString: (const char*)string_
 {
-	size_t len;
+	size_t length_;
 
 	[self freeMemory: string];
 
-	len = strlen(string_);
+	length_ = strlen(string_);
 
-	switch (of_string_check_utf8(string_, len)) {
+	if (length_ >= 3 && !memcmp(string_, "\xEF\xBB\xBF", 3)) {
+		string_ += 3;
+		length_ -= 3;
+	}
+
+	switch (of_string_check_utf8(string_, length_)) {
 	case 0:
 		isUTF8 = NO;
 		break;
 	case 1:
 		isUTF8 = YES;
@@ -153,38 +158,46 @@
 		isUTF8 = NO;
 
 		@throw [OFInvalidEncodingException newWithClass: isa];
 	}
 
-	length = len;
+	length = length_;
 	string = [self allocMemoryWithSize: length + 1];
 	memcpy(string, string_, length + 1);
 }
 
 - (void)appendCString: (const char*)string_
 {
-	size_t len;
+	size_t length_ = strlen(string_);
 
-	len = strlen(string_);
+	if (length_ >= 3 && !memcmp(string_, "\xEF\xBB\xBF", 3)) {
+		string_ += 3;
+		length_ -= 3;
+	}
 
-	switch (of_string_check_utf8(string_, len)) {
+	switch (of_string_check_utf8(string_, length_)) {
 	case 1:
 		isUTF8 = YES;
 		break;
 	case -1:
 		@throw [OFInvalidEncodingException newWithClass: isa];
 	}
 
 	string = [self resizeMemory: string
-			     toSize: length + len + 1];
-	memcpy(string + length, string_, len + 1);
-	length += len;
+			     toSize: length + length_ + 1];
+	memcpy(string + length, string_, length_ + 1);
+	length += length_;
 }
 
 - (void)appendCString: (const char*)string_
 	   withLength: (size_t)length_
 {
+	if (length_ >= 3 && !memcmp(string_, "\xEF\xBB\xBF", 3)) {
+		string_ += 3;
+		length_ -= 3;
+	}
+
 	switch (of_string_check_utf8(string_, length_)) {
 	case 1:
 		isUTF8 = YES;
 		break;
 	case -1:

Index: tests/OFStringTests.m
==================================================================
--- tests/OFStringTests.m
+++ tests/OFStringTests.m
@@ -141,12 +141,12 @@
 					 @"file://testfile.txt"]
 			   encoding: OF_STRING_ENCODING_ISO_8859_1]) &&
 	    [s[1] isEqual: @"testäöü"])
 
 	TEST(@"-[appendCStringWithLength:]",
-	    R([s[0] appendCString: "foobarqux" + 3
-		       withLength: 3]) && [s[0] isEqual: @"foobar"])
+	    R([s[0] appendCString: "foo\xEF\xBB\xBF" "barqux" + 3
+		       withLength: 6]) && [s[0] isEqual: @"foobar"])
 
 	EXPECT_EXCEPTION(@"Detection of invalid UTF-8 encoding #1",
 	    OFInvalidEncodingException,
 	    [OFString stringWithCString: "\xE0\x80"])
 	EXPECT_EXCEPTION(@"Detection of invalid UTF-8 encoding #2",