diff --git a/src/finnish/MorphoFin.gf b/src/finnish/MorphoFin.gf
index 3d3742186..422a6dbee 100644
--- a/src/finnish/MorphoFin.gf
+++ b/src/finnish/MorphoFin.gf
@@ -155,9 +155,9 @@ resource MorphoFin = ResFin ** open Prelude in {
       silakk = init silakka ;
       silaka = init silakan ;
       silak  = init silaka ;
-      silakkaa = silakka + case o of {
-        "o" | "ö" => "t" + a ;  -- radiota
-        _ => a                  -- sammakkoa
+      silakkaa = silakka + case silakka of {
+        _ + #vowel + ("o" | "ö") => "t" + a ;  -- radiota
+        _ => a                               -- sammakkoa
         } ;
       silakoiden = case <silakoita : Str> of {
         _ + "i" + ("a" | "ä") =>                    -- asemia
@@ -859,6 +859,8 @@ resource MorphoFin = ResFin ** open Prelude in {
 -- Auxiliaries
 -----------------------------------------
 
+  vowel : pattern Str = #("a"|"e"|"i"|"o"|"u"|"y"|"ä"|"ö") ;
+
 -- The following function defines how grade alternation works if it is active.
 -- In general, *whether there is* grade alternation must be given in the lexicon
 -- (cf. "auto - auton" not "audon"; "vihje - vihjeen" not "vihkeen").