diff --git a/asciidoctor.py b/asciidoctor.py
index 5d3df32..1539206 100644
--- a/asciidoctor.py
+++ b/asciidoctor.py
@@ -17,6 +17,7 @@ from pelican.readers import BaseReader
 from pelican.generators import Generator
 from pelican import signals
 import os
+import os.path
 import re
 import subprocess
 import sys
@@ -139,12 +140,13 @@ class AsciiDoctorPdfGenerator(Generator):
         filename = "{id_file}.pdf".format(id_file=content.slug)
         filepath = os.path.join(output_dir, filename)
 
-        check_call([cmd] + self.settings.get('ASCIIDOCTOR_EXTRA_OPTIONS', []) +
-                   ['--require', 'asciidoctor-pdf', '--backend', 'pdf'] +
-                   ['--doctype=article'] +
-                   ['--out-file', filepath, content.source_path])
-
-        logger.info("[ok] writing {filepath}".format(filepath=filepath))
+        if ((not os.path.isfile(filepath)) or
+            (os.path.getmtime(filepath) < os.path.getmtime(content.source_path))):
+            check_call([cmd] + self.settings.get('ASCIIDOCTOR_EXTRA_OPTIONS', []) +
+                       ['--require', 'asciidoctor-pdf', '--backend', 'pdf'] +
+                       ['--doctype=article'] +
+                       ['--out-file', filepath, content.source_path])
+            logger.info("[ok] writing {filepath}".format(filepath=filepath))
 
     def generate_output(self, writer=None):
         """Generate files for each articles and pages.