Index: src/OFMutableString.h
==================================================================
--- src/OFMutableString.h
+++ src/OFMutableString.h
@@ -76,21 +76,21 @@
  * Appends a formatted UTF-8 encoded C string to the OFString.
  * See printf for the format syntax.
  *
  * \param fmt A format string which generates the string to append
  */
-- appendWithFormat: (OFString*)fmt, ...;
+- appendFormat: (OFString*)fmt, ...;
 
 /**
  * Appends a formatted UTF-8 encoded C string to the OFString.
  * See printf for the format syntax.
  *
  * \param fmt A format string which generates the string to append
  * \param args The arguments used in the format string
  */
-- appendWithFormat: (OFString*)fmt
-	 arguments: (va_list)args;
+-  appendFormat: (OFString*)fmt
+  withArguments: (va_list)args;
 
 /**
  * Reverse the OFString.
  */
 - reverse;

Index: src/OFMutableString.m
==================================================================
--- src/OFMutableString.m
+++ src/OFMutableString.m
@@ -233,37 +233,39 @@
 		is_utf8 = YES;
 
 	return self;
 }
 
-- appendWithFormat: (OFString*)fmt, ...
+- appendFormat: (OFString*)fmt, ...
 {
 	id ret;
 	va_list args;
 
 	va_start(args, fmt);
-	ret = [self appendWithFormat: fmt
-			   arguments: args];
+	ret = [self appendFormat: fmt
+		   withArguments: args];
 	va_end(args);
 
 	return ret;
 }
 
-- appendWithFormat: (OFString*)fmt
-	 arguments: (va_list)args
+-  appendFormat: (OFString*)fmt
+  withArguments: (va_list)args
 {
 	char *t;
 
-	if (fmt == NULL)
-		@throw [OFInvalidFormatException newWithClass: isa];
+	if (fmt == nil)
+		@throw [OFInvalidArgumentException newWithClass: isa
+						       selector: _cmd];
 
-	if ((vasprintf(&t, [fmt cString], args)) == -1)
+	if ((vasprintf(&t, [fmt cString], args)) == -1) {
 		/*
 		 * This is only the most likely error to happen. Unfortunately,
 		 * there is no good way to check what really happened.
 		 */
 		@throw [OFOutOfMemoryException newWithClass: isa];
+	}
 
 	@try {
 		[self appendCString: t];
 	} @finally {
 		free(t);

Index: src/OFString.m
==================================================================
--- src/OFString.m
+++ src/OFString.m
@@ -454,14 +454,15 @@
 	int t;
 	Class c;
 
 	self = [super init];
 
-	if (fmt == NULL) {
+	if (fmt == nil) {
 		c = isa;
 		[super dealloc];
-		@throw [OFInvalidFormatException newWithClass: c];
+		@throw [OFInvalidArgumentException newWithClass: c
+						       selector: _cmd];
 	}
 
 	if ((t = vasprintf(&string, [fmt cString], args)) == -1) {
 		c = isa;
 		[super dealloc];

Index: tests/OFString.m
==================================================================
--- tests/OFString.m
+++ tests/OFString.m
@@ -139,12 +139,12 @@
 
 	TEST(@"+[stringWithFormat:]",
 	    [(s[0] = [OFMutableString stringWithFormat: @"%s: %d", "test", 123])
 	    isEqual: @"test: 123"])
 
-	TEST(@"-[appendWithFormat:]",
-	    [([s[0] appendWithFormat: @"%02X", 15]) isEqual: @"test: 1230F"])
+	TEST(@"-[appendFormat:]",
+	    [([s[0] appendFormat: @"%02X", 15]) isEqual: @"test: 1230F"])
 
 	TEST(@"-[indexOfFirstOccurrenceOfString:]",
 	    [@"𝄞öö" indexOfFirstOccurrenceOfString: @"öö"] == 1 &&
 	    [@"𝄞öö" indexOfFirstOccurrenceOfString: @"ö"] == 1 &&
 	    [@"𝄞öö" indexOfFirstOccurrenceOfString: @"𝄞"] == 0 &&