diff --git a/lacosmic/core.py b/lacosmic/core.py
index 30caea1..605d216 100644
--- a/lacosmic/core.py
+++ b/lacosmic/core.py
@@ -15,7 +15,7 @@
 def lacosmic(data, contrast, cr_threshold, neighbor_threshold,
              error=None, mask=None, background=None, effective_gain=None,
              readnoise=None, maxiter=4, border_mode='mirror'):
-    """
+    r"""
     Remove cosmic rays from an astronomical image using the L.A.Cosmic
     algorithm.
 
@@ -38,7 +38,7 @@ def lacosmic(data, contrast, cr_threshold, neighbor_threshold,
         image is oversampled, use a value between 1 and 2.  For details,
         please see `PASP 113, 1420 (2001)
         <https://ui.adsabs.harvard.edu/abs/2001PASP..113.1420V/abstract>`_,
-        which calls this parameter :math:`f_{\\mbox{lim}}`.  In
+        which calls this parameter :math:`f_{\mbox{lim}}`.  In
         particular, Figure 4 shows the approximate relationship between
         the ``contrast`` parameter and the full-width half-maximum (in
         pixels) of stars in your image.
diff --git a/setup.cfg b/setup.cfg
index cccd08b..8654f39 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -26,15 +26,17 @@ packages = find:
 python_requires = >=3.8
 setup_requires = setuptools_scm
 install_requires =
-    astropy >= 4.1
-    numpy >= 1.18
-    scipy >= 1.6.0
+    astropy>=4.1
+    numpy>=1.18
+    scipy>=1.6.0
 
 [options.extras_require]
 test =
     pytest-astropy
 docs =
+    sphinx
     sphinx-astropy
+    matplotlib>=3.1
 
 [options.package_data]
 lacosmic = data/*