diff --git a/openmc/config.py b/openmc/config.py
index a883c74cc..65b7e0863 100644
--- a/openmc/config.py
+++ b/openmc/config.py
@@ -21,6 +21,9 @@ class _Config(MutableMapping):
             # Force environment variable to match
             self._mapping[key] = Path(value)
             os.environ['OPENMC_CROSS_SECTIONS'] = str(value)
+        elif key == 'mg_cross_sections':
+            self._mapping[key] = Path(value)
+            os.environ['OPENMC_MG_CROSS_SECTIONS'] = str(value)
         elif key == 'chain_file':
             self._mapping[key] = Path(value)
         else:
@@ -40,7 +43,10 @@ class _Config(MutableMapping):
 config = _Config()
 
 # Set cross sections using environment variable
-config['cross_sections'] = os.environ.get("OPENMC_CROSS_SECTIONS")
+if "OPENMC_CROSS_SECTIONS" in os.environ:
+    config['cross_sections'] = os.environ["OPENMC_CROSS_SECTIONS"]
+if "OPENMC_MG_CROSS_SECTIONS" in os.environ:
+    config['mg_cross_sections'] = os.environ["OPENMC_MG_CROSS_SECTIONS"]
 
 # Check for depletion chain in cross_sections.xml
 # Set depletion chain
@@ -51,4 +57,5 @@ if chain_file is None and config['cross_sections'] is not None:
         if lib['type'] == 'depletion_chain':
             chain_file = lib['path']
             break
-config['chain_file'] = chain_file
+if chain_file is not None:
+    config['chain_file'] = chain_file
diff --git a/openmc/material.py b/openmc/material.py
index 96a660b8b..1b2b46a73 100644
--- a/openmc/material.py
+++ b/openmc/material.py
@@ -1329,10 +1329,11 @@ class Materials(cv.CheckedList):
     ----------
     cross_sections : str or path-like
         Indicates the path to an XML cross section listing file (usually named
-        cross_sections.xml). If it is not set, openmc.config['cross_sections']
-        will be used for continuous-energy calculations and
-        :envvar:`OPENMC_MG_CROSS_SECTIONS` will be used for multi-group
-        calculations to find the path to the HDF5 cross section file.
+        cross_sections.xml). If it is not set, the
+        :envvar:`OPENMC_CROSS_SECTIONS` environment variable will be used for
+        continuous-energy calculations and :envvar:`OPENMC_MG_CROSS_SECTIONS`
+        will be used for multi-group calculations to find the path to the HDF5
+        cross section file.
 
     """
 
diff --git a/openmc/mgxs_library.py b/openmc/mgxs_library.py
index 8d6e4bec9..98a99196e 100644
--- a/openmc/mgxs_library.py
+++ b/openmc/mgxs_library.py
@@ -1,6 +1,5 @@
 import copy
 from numbers import Real, Integral
-import os
 
 import h5py
 import numpy as np
@@ -2536,8 +2535,7 @@ class MGXSLibrary:
         ----------
         filename : str, optional
             Name of HDF5 file containing MGXS data. Default is None.
-            If not provided, the value of the OPENMC_MG_CROSS_SECTIONS
-            environmental variable will be used
+            If not provided, openmc.config['mg_cross_sections'] will be used.
 
         Returns
         -------
@@ -2545,15 +2543,14 @@ class MGXSLibrary:
             Multi-group cross section data object.
 
         """
-        # If filename is None, get the cross sections from the
-        # OPENMC_MG_CROSS_SECTIONS environment variable
+        # If filename is None, get the cross sections from openmc.config
         if filename is None:
-            filename = os.environ.get('OPENMC_MG_CROSS_SECTIONS')
+            filename = openmc.config.get('mg_cross_sections')
 
         # Check to make sure there was an environmental variable.
         if filename is None:
-            raise ValueError("Either path or OPENMC_MG_CROSS_SECTIONS "
-                             "environmental variable must be set")
+            raise ValueError("Either path or openmc.config['mg_cross_sections']"
+                             "must be set")
 
         check_type('filename', filename, str)
         file = h5py.File(filename, 'r')