diff --git a/src/czech/ResCze.gf b/src/czech/ResCze.gf
index 1ff5c71d9..3b77e73df 100644
--- a/src/czech/ResCze.gf
+++ b/src/czech/ResCze.gf
@@ -86,7 +86,7 @@ oper
     ul  + "ice" => ul + "ic" ;
     koleg + "yně" => koleg + "yň" ;
     ruz + "e" => ruz + "í" ;
-    _ => "??" + s  -- Predef.error ("shortFemPlGen does not apply to" ++ s)
+    _ => "" + s  -- Predef.error ("shortFemPlGen does not apply to" ++ s)
     } ;
 
 ---------------
@@ -155,7 +155,7 @@ oper
       <Neutr,       _ + "e"           , _+"ete"> => declKURE ;
       <Neutr,       _ + "e"           , _ + "e"> => declMORE ;
       <Neutr,       _ + "í"           , _ + "í"> => declSTAVENI ;
-      _ => (\s -> declSTROJ ("??" + s)) -- Predef.error ("cannot infer declension type for" ++ nom ++ gen)
+      _ => (\s -> declSTROJ ("" + s)) -- Predef.error ("cannot infer declension type for" ++ nom ++ gen)
       }
     in decl nom ;
 
@@ -172,7 +172,7 @@ oper
       _ + "ce"           => declSOUDCE s ;
       _ + "e"            => declMORE s ;
       _ + "í"            => declSTAVENI s ;
-      _ => declSTROJ ("??" + s) -- Predef.error ("cannot guess declension type for" ++ s)
+      _ => declSTROJ ("" + s) -- Predef.error ("cannot guess declension type for" ++ s)
       } ;
 
 -- the traditional declensions, in both CEG and Wiki
diff --git a/src/slovak/ResSlo.gf b/src/slovak/ResSlo.gf
index 531125255..c17132b1e 100644
--- a/src/slovak/ResSlo.gf
+++ b/src/slovak/ResSlo.gf
@@ -120,7 +120,7 @@ oper
       <Neutr,       _ + ("a"|"ä")             ,  _ + "iec">       => dievceniecN snom ;
       <Neutr,       _ + ("a"|"ä")             ,  _        >       => dievcaN snom ;
 
-      _ => dubN ("??"+snom) ** {pgen = pgen} ---- Predef.error ("cannot infer declension type for" ++ snom ++ pgen)
+      _ => dubN (""+snom) ** {pgen = pgen} ---- Predef.error ("cannot infer declension type for" ++ snom ++ pgen)
       } ** {pgen = pgen ; g = g} ;
 
 -- the "smartest" one-argument mkN
@@ -140,7 +140,7 @@ oper
         _ + "e"                     => srdceN snom ;
         _ + "ä"                     => dievcaN snom ;
 
-        _ => dubN ("??"+snom) ---- Predef.error ("cannot guess declension type for" ++ snom)
+        _ => dubN (""+snom) ---- Predef.error ("cannot guess declension type for" ++ snom)
       } ;
 
 
@@ -497,7 +497,7 @@ adjFormsAdjective : AdjForms -> Adjective = \afs -> {
         _ + "í"  => cudziA s ;
         _ + "i"  => rydziA s ;
         _ + ("ov"|"in") => otcovA s ;
-        _ => otcovA ("??"+s)  ---- Predef.error ("no mkA for" ++ s)
+        _ => otcovA (""+s)  ---- Predef.error ("no mkA for" ++ s)
         } ;