diff --git a/src/config.hpp b/src/config.hpp
index 83e612ac..0fe7c575 100644
--- a/src/config.hpp
+++ b/src/config.hpp
@@ -62,6 +62,10 @@ namespace zmq
         //  Maximal delta between high and low watermark.
         max_wm_delta = 1024,
 
+        //  Swap inteligently batches data for writing to disk. The size of
+        //  the batch in bytes is specified by this option.
+        swap_block_size = 8192,
+
         //  Maximum number of events the I/O thread can process in one go.
         max_io_events = 256,
 
diff --git a/src/swap.cpp b/src/swap.cpp
index cf735762..7a2234d4 100644
--- a/src/swap.cpp
+++ b/src/swap.cpp
@@ -36,16 +36,17 @@
 #include <algorithm>
 
 #include "swap.hpp"
+#include "config.hpp"
 #include "atomic_counter.hpp"
 #include "err.hpp"
 
-zmq::swap_t::swap_t (int64_t filesize_, size_t block_size_) :
+zmq::swap_t::swap_t (int64_t filesize_) :
     fd (-1),
     filesize (filesize_),
     file_pos (0),
     write_pos (0),
     read_pos (0),
-    block_size (block_size_),
+    block_size (swap_block_size),
     write_buf_start_addr (0)
 {
     zmq_assert (filesize > 0);
diff --git a/src/swap.hpp b/src/swap.hpp
index c9dfd997..76ad339c 100644
--- a/src/swap.hpp
+++ b/src/swap.hpp
@@ -38,7 +38,7 @@ namespace zmq
         enum { default_block_size = 8192 };
 
         //  Creates the swap.
-        swap_t (int64_t filesize_, size_t block_size_ = default_block_size);
+        swap_t (int64_t filesize_);
 
         ~swap_t ();