diff --git a/server/frontend.py b/server/frontend.py
index 01142a5..25aeba3 100644
--- a/server/frontend.py
+++ b/server/frontend.py
@@ -200,18 +200,6 @@
                         when calling the `get_stable_version` RPC.
     """
 
-    # DEFAULT_BOARD - The stable_version RPC API recognizes this special
-    # name as a mapping to use when no specific mapping for a board is
-    # present.  This default mapping is only allowed for CrOS image
-    # types; other image type subclasses exclude it.
-    #
-    # TODO(jrbarnette):  This value is copied from
-    # site_utils.stable_version_utils, because if we import that
-    # module here, it breaks unit tests.  Something about the Django
-    # setup...
-    DEFAULT_BOARD = 'DEFAULT'
-
-
     def __init__(self, afe, android):
         self._afe = afe
         self._android = android
@@ -276,21 +264,21 @@
     Abstract stable version mapping for full OS images of various types.
     """
 
+    def _version_is_valid(self, version):
+        return True
+
     def get_all_versions(self):
-        # TODO(jrbarnette):  We exclude non-OS (i.e. firmware) version
-        # mappings, but the returned dict doesn't distinguish CrOS
-        # boards from Android boards; both will be present, and the
-        # subclass can't distinguish them.
-        #
-        # Ultimately, the right fix is to move knowledge of image type
-        # over to the RPC server side.
-        #
         versions = super(_OSVersionMap, self).get_all_versions()
         for board in versions.keys():
-            if '/' in board:
+            if ('/' in board
+                    or not self._version_is_valid(versions[board])):
                 del versions[board]
         return versions
 
+    def get_version(self, board):
+        version = super(_OSVersionMap, self).get_version(board)
+        return version if self._version_is_valid(version) else None
+
 
 def format_cros_image_name(board, version):
     """
@@ -321,6 +309,9 @@
     def __init__(self, afe):
         super(_CrosVersionMap, self).__init__(afe, False)
 
+    def _version_is_valid(self, version):
+        return version is not None and '/' not in version
+
     def get_image_name(self, board):
         """
         Return the full image name of the stable version for `board`.
@@ -346,11 +337,8 @@
     def __init__(self, afe):
         super(_AndroidVersionMap, self).__init__(afe, True)
 
-
-    def get_all_versions(self):
-        versions = super(_AndroidVersionMap, self).get_all_versions()
-        del versions[self.DEFAULT_BOARD]
-        return versions
+    def _version_is_valid(self, version):
+        return version is not None and '/' in version
 
 
 class _SuffixHackVersionMap(_StableVersionMap):