diff --git a/prelude/Predef.gf b/prelude/Predef.gf
index a52f954d0..d8141ea8c 100644
--- a/prelude/Predef.gf
+++ b/prelude/Predef.gf
@@ -11,9 +11,11 @@ resource Predef = {
 
   param PBool = PTrue | PFalse ;
 
-  oper Int  : Type = variants {} ;                     -- the type of integers
-  oper Ints : Int -> Type = variants {} ;              -- the type of integers from 0 to n
+  oper Error : Type = variants {} ;          -- the empty type
+  oper Int   : Type = variants {} ;          -- the type of integers
+  oper Ints  : Int -> Type = variants {} ;   -- the type of integers from 0 to n
 
+  oper error  : Str        -> Error    = variants {} ; -- forms error message
   oper length : Tok ->        Int      = variants {} ; -- length of string
   oper drop   : Int -> Tok -> Tok      = variants {} ; -- drop prefix of length
   oper take   : Int -> Tok -> Tok      = variants {} ; -- take prefix of length
diff --git a/resource-1.0/english/ParadigmsEng.gf b/resource-1.0/english/ParadigmsEng.gf
index d03c3e2b9..c4b647c95 100644
--- a/resource-1.0/english/ParadigmsEng.gf
+++ b/resource-1.0/english/ParadigmsEng.gf
@@ -418,8 +418,13 @@ oper
     in mkV cry cries cried cried crying ;
 
   regDuplV fit = 
-    let fitt = fit + last fit in
-    mkV fit (fit + "s") (fitt + "ed") (fitt + "ed") (fitt + "ing") ;
+    case last fit of {
+      ("a" | "e" | "i" | "o" | "u" | "y") => 
+        Predef.error (["final duplication makes no sense for"] ++ fit) ;
+      t =>
+       let fitt = fit + t in
+       mkV fit (fit + "s") (fitt + "ed") (fitt + "ed") (fitt + "ing")
+      } ;
 
   irregV x y z = let reg = (regV x).s in
     mkV x (reg ! VPres) y z (reg ! VPresPart) ** {s1 = [] ; lock_V = <>} ;