Index: src/OFString.h
==================================================================
--- src/OFString.h
+++ src/OFString.h
@@ -667,10 +667,18 @@
  * @param string The string to append
  * @return A new, autoreleased OFString with the specified string appended
  */
 - (OFString*)stringByAppendingString: (OFString*)string;
 
+/*!
+ * @brief Creates a new string by appending the specified format.
+ *
+ * @param format A format string which generates the string to append
+ * @return A new, autoreleased OFString with the specified format appended
+ */
+- (OFString*)stringByAppendingFormat: (OFConstantString*)format, ...;
+
 /*!
  * @brief Creates a new string by appending a path component.
  *
  * @param component The path component to append
  * @return A new, autoreleased OFString with the path component appended

Index: src/OFString.m
==================================================================
--- src/OFString.m
+++ src/OFString.m
@@ -1287,10 +1287,27 @@
 {
 	OFMutableString *new;
 
 	new = [OFMutableString stringWithString: self];
 	[new appendString: string];
+
+	[new makeImmutable];
+
+	return new;
+}
+
+- (OFString*)stringByAppendingFormat: (OFConstantString*)format, ...
+{
+	OFMutableString *new;
+	va_list arguments;
+
+	new = [OFMutableString stringWithString: self];
+
+	va_start(arguments, format);
+	[new appendFormat: format
+		arguments: arguments];
+	va_end(arguments);
 
 	[new makeImmutable];
 
 	return new;
 }