diff --git a/Documentation/conf.py b/Documentation/conf.py
index f82fa0e18295..3180fd972003 100644
--- a/Documentation/conf.py
+++ b/Documentation/conf.py
@@ -48,7 +48,7 @@ try:
 except ImportError:
     print("Error: Please install sphinxcontrib.ditaa for ASCII art conversion\n")
 else:
-    extensions += 'sphinxcontrib.ditaa'
+    extensions += ['sphinxcontrib.ditaa']
 
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.