diff --git a/src/GF/Speech/CFG.hs b/src/GF/Speech/CFG.hs
index 52db2827a..254024f5c 100644
--- a/src/GF/Speech/CFG.hs
+++ b/src/GF/Speech/CFG.hs
@@ -237,6 +237,13 @@ allRulesGrouped = Map.toList . Map.map Set.toList . cfgRules
 allCats :: CFG -> [Cat]
 allCats = Map.keys . cfgRules
 
+-- | Gets all categories which have rules or occur in a RHS.
+allCats' :: CFG -> [Cat]
+allCats' cfg = Set.toList (Map.keysSet (cfgRules cfg) `Set.union` 
+                           Set.fromList [c | rs <- Map.elems (cfgRules cfg), 
+                                             r  <- Set.toList rs, 
+                                             NonTerminal c <- ruleRhs r])
+
 -- | Gets all rules for the given category.
 catRules :: CFG -> Cat -> [CFRule]
 catRules gr c = Set.toList $ Map.findWithDefault Set.empty c (cfgRules gr)
diff --git a/src/GF/Speech/SRG.hs b/src/GF/Speech/SRG.hs
index 622ba4ca3..03f6c0be7 100644
--- a/src/GF/Speech/SRG.hs
+++ b/src/GF/Speech/SRG.hs
@@ -128,7 +128,7 @@ renameCats prefix cfg = mapCFGCats renameCat cfg
   where renameCat c | isExternal c = c ++ "_cat"
                     | otherwise = Map.findWithDefault (badCat c) c names
         isExternal c = c `Set.member` cfgExternalCats cfg        
-        catsByPrefix = buildMultiMap [(takeWhile (/='_') cat, cat) | cat <- allCats cfg, not (isExternal cat)]
+        catsByPrefix = buildMultiMap [(takeWhile (/='_') cat, cat) | cat <- allCats' cfg, not (isExternal cat)]
         names = Map.fromList [(c,pref++"_"++show i) | (pref,cs) <- catsByPrefix, (c,i) <- zip cs [1..]]
         badCat c = error ("GF.Speech.SRG.renameCats: " ++ c ++ "\n" ++ prCFG cfg)