Index: src/OFMutableData.h
==================================================================
--- src/OFMutableData.h
+++ src/OFMutableData.h
@@ -155,10 +155,18 @@
  */
 - (void)insertItems: (const void *)items
 	    atIndex: (size_t)index
 	      count: (size_t)count;
 
+/*!
+ * @brief Increases the count by the specified number. The new items are all
+ *	  filled with null bytes.
+ *
+ * @param count The count by which to increase the count
+ */
+- (void)increaseCountBy: (size_t)count;
+
 /*!
  * @brief Removes the item at the specified index.
  *
  * @param index The index of the item to remove
  */

Index: src/OFMutableData.m
==================================================================
--- src/OFMutableData.m
+++ src/OFMutableData.m
@@ -217,10 +217,26 @@
 	    _items + index * _itemSize, (_count - index) * _itemSize);
 	memcpy(_items + index * _itemSize, items, count * _itemSize);
 
 	_count += count;
 }
+
+- (void)increaseCountBy: (size_t)count
+{
+	if (count > SIZE_MAX - _count)
+		@throw [OFOutOfRangeException exception];
+
+	if (_count + count > _capacity) {
+		_items = [self resizeMemory: _items
+				       size: _itemSize
+				      count: _count + count];
+		_capacity = _count + count;
+	}
+
+	memset(_items + _count * _itemSize, '\0', count * _itemSize);
+	_count += count;
+}
 
 - (void)removeItemAtIndex: (size_t)index
 {
 	[self removeItemsInRange: of_range(index, 1)];
 }