diff --git a/CHANGES b/CHANGES
index 3e08091857..4d17a0c645 100644
--- a/CHANGES
+++ b/CHANGES
@@ -15,6 +15,8 @@ Bugs fixed
 * #1374: Fix for autosummary generating overly-long summaries if first line
   doesn't end with a period.
 * #1383: Fix Python 2.5 compatibility of sphinx-apidoc.
+* #1391: Actually prevent using "pngmath" and "mathjax" extensions at the same
+  time in sphinx-quickstart.
 
 Documentation
 -------------
diff --git a/sphinx/quickstart.py b/sphinx/quickstart.py
index 8ea5b3a308..5cf067e96b 100644
--- a/sphinx/quickstart.py
+++ b/sphinx/quickstart.py
@@ -1141,6 +1141,7 @@ Please indicate if you want to use one of the following Sphinx extensions:'''
     if d['ext_pngmath'] and d['ext_mathjax']:
         print '''Note: pngmath and mathjax cannot be enabled at the same time.
 pngmath has been deselected.'''
+        d['ext_pngmath'] = False
     if 'ext_ifconfig' not in d:
         do_prompt(d, 'ext_ifconfig', 'ifconfig: conditional inclusion of '
                   'content based on config values (y/n)', 'n', boolean)