diff --git a/src/calibre/constants.py b/src/calibre/constants.py
index 8c330d8006..f69668ffe1 100644
--- a/src/calibre/constants.py
+++ b/src/calibre/constants.py
@@ -28,6 +28,7 @@ isunix = isosx or islinux
 isportable = os.environ.get('CALIBRE_PORTABLE_BUILD', None) is not None
 ispy3 = sys.version_info.major > 2
 isxp = iswindows and sys.getwindowsversion().major < 6
+is64bit = sys.maxint > (1 << 32)
 isworker = os.environ.has_key('CALIBRE_WORKER') or os.environ.has_key('CALIBRE_SIMPLE_WORKER')
 if isworker:
     os.environ.pop('CALIBRE_FORCE_ANSI', None)
@@ -172,6 +173,9 @@ def get_version():
     v = __version__
     if getattr(sys, 'frozen', False) and dv and os.path.abspath(dv) in sys.path:
         v += '*'
+    if iswindows and is64bit:
+        v += ' [64bit]'
+
     return v
 
 def get_portable_base():