diff --git a/youtube_dl/postprocessor/execafterdownload.py b/youtube_dl/postprocessor/execafterdownload.py
index da60671d2..0d19f1d1e 100644
--- a/youtube_dl/postprocessor/execafterdownload.py
+++ b/youtube_dl/postprocessor/execafterdownload.py
@@ -1,6 +1,7 @@
 from __future__ import unicode_literals
 
 import subprocess
+import sys
 
 from .common import PostProcessor
 from ..compat import compat_shlex_quote
@@ -17,14 +18,14 @@ class ExecAfterDownloadPP(PostProcessor):
 
     def run(self, information):
         cmd = self.exec_cmd
-        info = {}
-
-        for key in information:
-            value = information[key]
-            info[key] = compat_shlex_quote(value) if isinstance(value, (str, unicode)) else value
 
         # expose info to exec argument
         # youtube-dl -x -o "%(playlist_index)s - %(title)s.%(ext)s" --exec "id3v2 -T {0[playlist_index]} -t {0[title]} {0[filepath]}" PLAYLIST_ID
+        str_types = (str) if sys.version_info.major > 2 else (str, unicode)
+        info = {}
+        for key in information:
+            value = information[key]
+            info[key] = compat_shlex_quote(value) if isinstance(value, str_types) else value
         cmd = cmd.format(info)
 
         self._downloader.to_screen('[exec] Executing command: %s' % cmd)