diff --git a/configure.ac b/configure.ac
index 19759a9e..b4a4d2d6 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1,6 +1,6 @@
 AC_INIT(rtorrent, 0.9.1, jaris@ifi.uio.no)
 
-AC_DEFINE(API_VERSION, 3, api version)
+AC_DEFINE(API_VERSION, 4, api version)
 
 AM_INIT_AUTOMAKE
 AM_CONFIG_HEADER(config.h)
diff --git a/src/command_download.cc b/src/command_download.cc
index 14394e6a..33f876fb 100644
--- a/src/command_download.cc
+++ b/src/command_download.cc
@@ -334,8 +334,14 @@ d_chunks_seen(core::Download* download) {
 
   if (seen == NULL)
     return std::string();
-  else
-    return std::string((const char*)seen, download->download()->file_list()->size_chunks());
+
+  uint32_t size = download->download()->file_list()->size_chunks();
+
+  std::string result;
+  result.resize(size * 2);
+
+  rak::transform_hex((const char*)seen, (const char*)seen + size, result.begin());
+  return result;
 }
 
 torrent::Object