diff --git a/tempest/common/api_version_request.py b/tempest/common/api_version_request.py
index 72a11ea..d8a5b56 100644
--- a/tempest/common/api_version_request.py
+++ b/tempest/common/api_version_request.py
@@ -54,6 +54,8 @@
             None value should be used to create Null APIVersionRequest,
             which is equal to 0.0
         """
+        # NOTE(gmann): 'version_string' as String "None" will be considered as
+        # invalid version string.
         self.ver_major = 0
         self.ver_minor = 0
 
diff --git a/tempest/config.py b/tempest/config.py
index 26dda2d..a6212fb 100644
--- a/tempest/config.py
+++ b/tempest/config.py
@@ -347,16 +347,18 @@
                     "The format is 'X.Y', where 'X' and 'Y' are int values. "
                     "Tempest selects tests based on the range between "
                     "min_microversion and max_microversion. "
-                    "If both values are None, Tempest avoids tests which "
-                    "require a microversion."),
+                    "If both values are not specified, Tempest avoids tests "
+                    "which require a microversion. Valid values are string "
+                    "with format 'X.Y' or string 'latest'"),
     cfg.StrOpt('max_microversion',
                default=None,
                help="Upper version of the test target microversion range. "
                     "The format is 'X.Y', where 'X' and 'Y' are int values. "
                     "Tempest selects tests based on the range between "
                     "min_microversion and max_microversion. "
-                    "If both values are None, Tempest avoids tests which "
-                    "require a microversion."),
+                    "If both values are not specified, Tempest avoids tests "
+                    "which require a microversion. Valid values are string "
+                    "with format 'X.Y' or string 'latest'"),
     cfg.BoolOpt('disk_config',
                 default=True,
                 help="If false, skip disk config tests"),
diff --git a/tempest/exceptions.py b/tempest/exceptions.py
index 8537898..1d725af 100644
--- a/tempest/exceptions.py
+++ b/tempest/exceptions.py
@@ -177,8 +177,8 @@
 
 
 class InvalidAPIVersionString(TempestException):
-    msg_fmt = ("API Version String %(version)s is of invalid format. Must "
-               "be of format MajorNum.MinorNum.")
+    message = ("API Version String %(version)s is of invalid format. Must "
+               "be of format MajorNum.MinorNum or string 'latest'.")
 
 
 class CommandFailed(Exception):