Index: src/OFConstantString.m
==================================================================
--- src/OFConstantString.m
+++ src/OFConstantString.m
@@ -85,10 +85,15 @@
 - initWithString: (OFString*)str
 {
 	@throw [OFNotImplementedException newWithClass: isa
 					      selector: _cmd];
 }
+
+- (BOOL)isUTF8
+{
+	return YES;
+}
 
 - (void)addMemoryToPool: (void*)ptr
 {
 	@throw [OFNotImplementedException newWithClass: isa
 					      selector: _cmd];

Index: src/OFString.h
==================================================================
--- src/OFString.h
+++ src/OFString.h
@@ -265,10 +265,14 @@
 
 /**
  * \return The length of the string which cString would return
  */
 - (size_t)cStringLength;
+
+/// \cond internal
+- (BOOL)isUTF8;
+/// \endcond
 
 /**
  * Compares the OFString to another OFString.
  *
  * \param str A string to compare with

Index: src/OFString.m
==================================================================
--- src/OFString.m
+++ src/OFString.m
@@ -14,10 +14,11 @@
 #define _GNU_SOURCE
 #include <stdarg.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <ctype.h>
 
 #include <sys/stat.h>
 #ifdef HAVE_MADVISE
 # include <sys/mman.h>
 #else
@@ -34,10 +35,25 @@
 #import "asprintf.h"
 #import "unicode.h"
 
 extern const uint16_t of_iso_8859_15[256];
 extern const uint16_t of_windows_1252[256];
+
+static inline int
+memcasecmp(const char *s1, const char *s2, size_t len)
+{
+	size_t i;
+
+	for (i = 0; i < len; i++) {
+		if (tolower(s1[i]) > tolower(s2[i]))
+			return OF_ORDERED_DESCENDING;
+		if (tolower(s1[i]) < tolower(s2[i]))
+			return OF_ORDERED_ASCENDING;
+	}
+
+	return OF_ORDERED_SAME;
+}
 
 /* References for static linking */
 void _references_to_categories_of_OFString()
 {
 	_OFString_Hashing_reference = 1;
@@ -700,10 +716,15 @@
 
 - (size_t)cStringLength
 {
 	return length;
 }
+
+- (BOOL)isUTF8
+{
+	return isUTF8;
+}
 
 - (BOOL)isEqual: (OFObject*)obj
 {
 	if (![obj isKindOfClass: [OFString class]])
 		return NO;
@@ -723,12 +744,12 @@
 	return [[OFMutableString alloc] initWithString: self];
 }
 
 - (of_comparison_result_t)compare: (OFString*)str
 {
-	int cmp;
 	size_t str_len, min_len;
+	int cmp;
 
 	if (![str isKindOfClass: [OFString class]])
 		@throw [OFInvalidArgumentException newWithClass: isa
 						       selector: _cmd];
 
@@ -750,18 +771,36 @@
 }
 
 - (of_comparison_result_t)caseInsensitiveCompare: (OFString*)str
 {
 	const char *str_cstr;
-	size_t i, j, str_len;
+	size_t i, j, str_len, min_len;
+	int cmp;
 
 	if (![str isKindOfClass: [OFString class]])
 		@throw [OFInvalidArgumentException newWithClass: isa
 						       selector: _cmd];
 
 	str_cstr = [str cString];
 	str_len = [str cStringLength];
+
+	if (![self isUTF8]) {
+		min_len = (length > str_len ? str_len : length);
+
+		if ((cmp = memcasecmp(string, [str cString], min_len)) == 0) {
+			if (length > str_len)
+				return OF_ORDERED_DESCENDING;
+			if (length < str_len)
+				return OF_ORDERED_ASCENDING;
+			return OF_ORDERED_SAME;
+		}
+
+		if (cmp > 0)
+			return OF_ORDERED_DESCENDING;
+		else
+			return OF_ORDERED_ASCENDING;
+	}
 
 	i = j = 0;
 
 	while (i < length && j < str_len) {
 		of_unichar_t c1, c2;
@@ -820,10 +859,17 @@
 }
 
 - (of_unichar_t)characterAtIndex: (size_t)index
 {
 	of_unichar_t c;
+
+	if (![self isUTF8]) {
+		if (index >= length)
+			@throw [OFOutOfRangeException newWithClass: isa];
+
+		return string[index];
+	}
 
 	index = of_string_index_to_position(string, index, length);
 
 	if (index >= length)
 		@throw [OFOutOfRangeException newWithClass: isa];
@@ -876,12 +922,14 @@
 }
 
 - (OFString*)substringFromIndex: (size_t)start
 			toIndex: (size_t)end
 {
-	start = of_string_index_to_position(string, start, length);
-	end = of_string_index_to_position(string, end, length);
+	if ([self isUTF8]) {
+		start = of_string_index_to_position(string, start, length);
+		end = of_string_index_to_position(string, end, length);
+	}
 
 	if (start > end)
 		@throw [OFInvalidArgumentException newWithClass: isa
 						       selector: _cmd];
 

Index: tests/OFStringTests.m
==================================================================
--- tests/OFStringTests.m
+++ tests/OFStringTests.m
@@ -72,11 +72,13 @@
 	    [@"a" caseInsensitiveCompare: @"A"] == OF_ORDERED_SAME &&
 	    [@"Ä" caseInsensitiveCompare: @"ä"] == OF_ORDERED_SAME &&
 	    [@"я" caseInsensitiveCompare: @"Я"] == OF_ORDERED_SAME &&
 	    [@"€" caseInsensitiveCompare: @"ß"] == OF_ORDERED_DESCENDING &&
 	    [@"ß" caseInsensitiveCompare: @"→"] == OF_ORDERED_ASCENDING &&
-	    [@"AA" caseInsensitiveCompare: @"z"] == OF_ORDERED_ASCENDING)
+	    [@"AA" caseInsensitiveCompare: @"z"] == OF_ORDERED_ASCENDING &&
+	    [[OFString stringWithCString: "ABC"] caseInsensitiveCompare:
+	    [OFString stringWithCString: "AbD"]] == [@"abc" compare: @"abd"])
 
 	TEST(@"-[hash] is the same if -[isEqual:] is YES",
 	    [s[0] hash] == [s[2] hash])
 
 	TEST(@"-[appendString:] and -[appendCString:]",