diff --git a/src/calibre/constants.py b/src/calibre/constants.py
index d5663d31f1..db6f54ce00 100644
--- a/src/calibre/constants.py
+++ b/src/calibre/constants.py
@@ -48,6 +48,18 @@ fcntl      = None if iswindows else importlib.import_module('fcntl')
 
 filesystem_encoding = sys.getfilesystemencoding()
 if filesystem_encoding is None: filesystem_encoding = 'utf-8'
+else:
+    try:
+        if codecs.lookup(filesystem_encoding).name == 'ascii':
+            filesystem_encoding = 'utf-8'
+            # On linux, unicode arguments to os file functions are coerced to an ascii
+            # bytestring if sys.getfilesystemencoding() == 'ascii', which is
+            # just plain dumb. So issue a warning.
+            print ('WARNING: You do not have the LANG environment variable set. '
+                    'This will cause problems with non-ascii filenames. '
+                    'Set it to something like en_US.UTF-8.\n')
+    except:
+        filesystem_encoding = 'utf-8'
 
 
 DEBUG = False