diff --git a/doc/conf.py b/doc/conf.py
index de898facf492671b8290c1d0ff3e9ffb2ca605e0..296afd789a1aa97f94d9d25e44744aae38b72767 100644
--- a/doc/conf.py
+++ b/doc/conf.py
@@ -50,7 +50,7 @@ nbsphinx_codecell_lexer = 'python3'
 intersphinx_mapping = {'python': ('https://docs.python.org/3.6', None),
                        'numpy': ('https://docs.scipy.org/doc/numpy/', None),
                        'matplotlib': ('https://matplotlib.org/', None),
-                       'sympy': ('https://docs.sympy.org/latest/', None),
+                       'sympy': ('https://docs.sympy.org/1.5.1/', None),
                        }
 
 autodoc_member_order = 'bysource'