diff --git a/src/calibre/ebooks/conversion/cli.py b/src/calibre/ebooks/conversion/cli.py
index 1c7a29d7ff..559402ca1c 100644
--- a/src/calibre/ebooks/conversion/cli.py
+++ b/src/calibre/ebooks/conversion/cli.py
@@ -68,8 +68,8 @@ def check_command_line_options(parser, args, log):
         raise SystemExit(1)
 
     output = args[2]
-    if output.startswith('.') and (output != '.' and not
-            output.startswith('..')):
+    if (output.startswith('.') and output[:2] not in {'..', '.'} and '/' not in
+            output and '\\' not in output):
         output = os.path.splitext(os.path.basename(input))[0]+output
     output = os.path.abspath(output)