Index: Source/Additions/GSCompatibility.m
===================================================================
--- Source/Additions/GSCompatibility.m	(Revision 28408)
+++ Source/Additions/GSCompatibility.m	(Arbeitskopie)
@@ -394,6 +394,7 @@
 
 @implementation NSString(GSCompatibility)
 
+#if OS_API_VERSION (MAC_OS_X_VERSION_10_2,MAC_OS_X_VERSION_10_5)
 // From GNUStep
 /**
  * If the string consists of the words 'true' or 'yes' (case insensitive)
@@ -402,16 +403,20 @@
  */
 - (BOOL) boolValue
 {
-  if ([self caseInsensitiveCompare: @"YES"] == NSOrderedSame)
+  static NSCharacterSet *yes = nil;
+
+  if (yes == nil)
     {
-        return YES;
+      yes = RETAIN([NSCharacterSet characterSetWithCharactersInString:
+      @"123456789yYtT"]);
     }
-  if ([self caseInsensitiveCompare: @"true"] == NSOrderedSame)
+  if ([self rangeOfCharacterFromSet: yes].length > 0)
     {
-        return YES;
+      return YES;
     }
-  return [self intValue] != 0 ? YES : NO;
+  return NO;
 }
+#endif
 
 - (NSString*) substringFromRange:(NSRange)range
 {