Index: libtorrent/src/data/socket_file.cc
===================================================================
--- libtorrent/src/data/socket_file.cc	(revision 827)
+++ libtorrent/src/data/socket_file.cc	(working copy)
@@ -162,20 +162,27 @@
 MemoryChunk
 SocketFile::create_chunk(uint64_t offset, uint32_t length, int prot, int flags) const {
   if (!is_open())
-    throw internal_error("SocketFile::get_chunk() called on a closed file");
+    throw internal_error("SocketFile::get_chunk() called on a closed file.");
 
   if (((prot & MemoryChunk::prot_read) && !is_readable()) ||
       ((prot & MemoryChunk::prot_write) && !is_writable()))
-    throw storage_error("SocketFile::get_chunk() permission denied");
+    throw storage_error("SocketFile::get_chunk() permission denied.");
 
+  uint64_t fileSize = size();
+
   // For some reason mapping beyond the extent of the file does not
   // cause mmap to complain, so we need to check manually here.
-  if (offset < 0 || length == 0 || offset > size() || offset + length > size())
+  if (offset < 0 || length == 0 || offset > fileSize || offset + length > fileSize)
     return MemoryChunk();
 
-  uint64_t align = offset % MemoryChunk::page_size();
+  uint64_t align     = offset % MemoryChunk::page_size();
+  uint64_t mapLength = std::min(((length + align + MemoryChunk::page_size() - 1) / MemoryChunk::page_size()) * MemoryChunk::page_size(),
+                                fileSize - (offset - align));
 
-  char* ptr = (char*)mmap(NULL, length + align, prot, flags, m_fd, offset - align);
+  if (offset - align + mapLength != fileSize && (offset - align + mapLength) % MemoryChunk::page_size() != 0)
+    throw internal_error("SocketFile::create_chunk(...) Length not page aligned.");
+
+  char* ptr = (char*)mmap(NULL, mapLength, prot, flags, m_fd, offset - align);
   
   if (ptr == MAP_FAILED)
     return MemoryChunk();