diff --git a/scripts/lib/CIME/XML/entry_id.py b/scripts/lib/CIME/XML/entry_id.py
index d488a5b2905..e7f0ac9796c 100644
--- a/scripts/lib/CIME/XML/entry_id.py
+++ b/scripts/lib/CIME/XML/entry_id.py
@@ -8,6 +8,7 @@
 from CIME.XML.generic_xml import GenericXML
 
 from copy import deepcopy
+import six
 
 logger = logging.getLogger(__name__)
 
@@ -229,7 +230,7 @@ def _set_value(self, node, value, vid=None, subgroup=None, ignore_type=False):
     def get_valid_value_string(self, node, value,vid=None,  ignore_type=False):
         valid_values = self._get_valid_values(node)
         if ignore_type:
-            expect(type(value) is str, "Value must be type string if ignore_type is true")
+            expect(isinstance(value, six.string_types), "Value must be type string if ignore_type is true")
             str_value = value
             return str_value
         type_str = self._get_type_info(node)
diff --git a/scripts/lib/CIME/XML/generic_xml.py b/scripts/lib/CIME/XML/generic_xml.py
index 770d4f006a6..0113433f7c6 100644
--- a/scripts/lib/CIME/XML/generic_xml.py
+++ b/scripts/lib/CIME/XML/generic_xml.py
@@ -209,7 +209,7 @@ def get_resolved_value(self, raw_value):
         if item_data is None:
             return None
 
-        if type(item_data) is not str:
+        if not isinstance(item_data, six.string_types):
             return item_data
 
         for m in env_ref_re.finditer(item_data):
diff --git a/scripts/lib/CIME/case.py b/scripts/lib/CIME/case.py
index 1f3c0a6c301..1cef50330ba 100644
--- a/scripts/lib/CIME/case.py
+++ b/scripts/lib/CIME/case.py
@@ -5,7 +5,7 @@
 through the Case module.
 """
 from copy import deepcopy
-import glob, os, shutil, math
+import glob, os, shutil, math, six
 from CIME.XML.standard_module_setup import *
 #pylint: disable=import-error,redefined-builtin
 from six.moves import input
@@ -250,7 +250,7 @@ def get_values(self, item, attribute=None, resolved=True, subgroup=None):
                 vtype = env_file.get_type_info(item)
                 if resolved:
                     for result in results:
-                        if type(result) is str:
+                        if isinstance(result, six.string_types):
                             result = self.get_resolved_value(result)
                             new_results.append(convert_to_type(result, vtype, item))
                         else:
@@ -264,7 +264,7 @@ def get_values(self, item, attribute=None, resolved=True, subgroup=None):
             if len(results) > 0:
                 if resolved:
                     for result in results:
-                        if type(result) is str:
+                        if isinstance(result, six.string_types):
                             new_results.append(self.get_resolved_value(result))
                         else:
                             new_results.append(result)
@@ -281,7 +281,7 @@ def get_value(self, item, attribute=None, resolved=True, subgroup=None):
             result = env_file.get_value(item, attribute, resolved=False, subgroup=subgroup)
 
             if result is not None:
-                if resolved and type(result) is str:
+                if resolved and isinstance(result, six.string_types):
                     result = self.get_resolved_value(result)
                     vtype = env_file.get_type_info(item)
                     if vtype is not None:
@@ -293,7 +293,7 @@ def get_value(self, item, attribute=None, resolved=True, subgroup=None):
             result = env_file.get_value(item, attribute, resolved=False, subgroup=subgroup)
 
             if result is not None:
-                if resolved and type(result) is str:
+                if resolved and isinstance(result, six.string_types):
                     return self.get_resolved_value(result)
                 return result
 
@@ -576,7 +576,7 @@ def get_compset_components(self):
     def __iter__(self):
         for entryid_file in self._env_entryid_files:
             for key, val in entryid_file:
-                if type(val) is str and '$' in val:
+                if isinstance(val, six.string_types) and '$' in val:
                     yield key, self.get_resolved_value(val)
                 else:
                     yield key, val
diff --git a/scripts/lib/CIME/case_setup.py b/scripts/lib/CIME/case_setup.py
index 23fe0902a57..88bbee08e2b 100644
--- a/scripts/lib/CIME/case_setup.py
+++ b/scripts/lib/CIME/case_setup.py
@@ -12,7 +12,7 @@
 from CIME.utils             import get_cime_root, run_and_log_case_status, get_model
 from CIME.test_status       import *
 
-import shutil
+import shutil, six
 
 logger = logging.getLogger(__name__)
 
@@ -80,7 +80,7 @@ def _case_setup_impl(case, caseroot, clean=False, test_mode=False, reset=False):
 
     # Check that userdefine settings are specified before expanding variable
     for vid, value in case:
-        expect(not (type(value) is str and "USERDEFINED_required_build" in value),
+        expect(not (isinstance(value, six.string_types) and "USERDEFINED_required_build" in value),
                "Parameter '{}' must be defined".format(vid))
 
     # Remove batch scripts
diff --git a/scripts/lib/CIME/compare_namelists.py b/scripts/lib/CIME/compare_namelists.py
index d4b0fca41b6..3e0c554beac 100644
--- a/scripts/lib/CIME/compare_namelists.py
+++ b/scripts/lib/CIME/compare_namelists.py
@@ -1,4 +1,4 @@
-import os, re, logging
+import os, re, logging, six
 
 from collections import OrderedDict
 from CIME.utils  import expect
@@ -365,7 +365,7 @@ def _compare_values(name, gold_value, comp_value, case):
                 comments += "  dict variable '{}' has extra key {} with value {}\n".format(name, key, comp_value[key])
 
     else:
-        expect(type(gold_value) is str, "Unexpected type found: '{}'".format(type(gold_value)))
+        expect(isinstance(gold_value, six.string_types), "Unexpected type found: '{}'".format(type(gold_value)))
         norm_gold_value = _normalize_string_value(name, gold_value, case)
         norm_comp_value = _normalize_string_value(name, comp_value, case)