--- a/doc/source/conf.py
+++ b/doc/source/conf.py
@@ -72,10 +72,14 @@ extensions = ['sphinx.ext.autodoc',
               'sphinx.ext.mathjax',
               'sphinx.ext.ifconfig',
               'sphinx.ext.linkcode',
-              'nbsphinx',
               ]
 
 mathjax_path='MathJax.js'
+try:
+    import nbsphinx
+    extensions += ['nbsphinx']
+except:
+    pass  # survive without
 
 exclude_patterns = ['**.ipynb_checkpoints']
 
