diff --git a/src/Text/ParserCombinators/UU/CHANGELOG.hs b/src/Text/ParserCombinators/UU/CHANGELOG.hs
--- a/src/Text/ParserCombinators/UU/CHANGELOG.hs
+++ b/src/Text/ParserCombinators/UU/CHANGELOG.hs
@@ -1,5 +1,9 @@
 -- | This module just contains the CHANGELOG
 --
+-- Version 2.7.3.1
+--
+-- fixed corner case when combining to failing parsers during grammar analysis; probably useful error message is now gone
+--
 -- Version 2.7.3
 --
 -- better behaviour when inserting at end of input
diff --git a/src/Text/ParserCombinators/UU/Core.hs b/src/Text/ParserCombinators/UU/Core.hs
--- a/src/Text/ParserCombinators/UU/Core.hs
+++ b/src/Text/ParserCombinators/UU/Core.hs
@@ -185,9 +185,10 @@
 -- | `mkParser` combines the non-empty descriptor part and the empty descriptor part into a descriptor tupled with the parser triple
 mkParser :: Maybe (T st a) -> Maybe a -> Nat -> P st a
 mkParser np ne  l  =  P (mkParser'  np ne)  np l ne
-  where  mkParser' np@(Just nt)  ne@Nothing   =  nt               
-         mkParser' np@Nothing    ne@(Just a)  =  pure a       
-         mkParser' np@(Just nt)  ne@(Just a)  =  nt <|> pure a
+  where  mkParser' np@(Just nt)  ne@Nothing    =  nt               
+         mkParser' np@Nothing    ne@(Just a)   =  pure a       
+         mkParser' np@(Just nt)  ne@(Just a)   =  nt <|> pure a
+         mkParser' np@(Nothing)  ne@(Nothing)  =  empty
 
 -- ! `combine` creates the non-empty parser 
 combine :: (Alternative f) => Maybe t1 -> Maybe t2 -> t -> Maybe t3
@@ -381,12 +382,12 @@
 -- By default we use the future parser, since this gives us access to partal
 -- result; future parsers are expected to run in less space.
 parse :: (Eof t) => P t a -> t -> a
-parse   (P (T _  pf _) _ _ _)  = fst . eval . pf  (\ rest   -> if eof rest then         Step 0 (Step 0 (Step 0 (Step 0 (error "ambiguous parser?"))))  
+parse   (P (T _  pf _) _ _ _)  = fst . eval . pf  (\ rest   -> if eof rest then  Step 0 ( Step 0 (Step 0 (Step 0 (Step 0 (error "ambiguous parser?"))))) 
                                                                else error "pEnd missing?")
 -- | The function @`parse_h`@ behaves like @`parse`@ but using the history
 -- parser. This parser does not give online results, but might run faster.
 parse_h :: (Eof t) => P t a -> t -> a
-parse_h (P (T ph _  _) _ _ _)  = fst . eval . ph  (\ a rest -> if eof rest then push a (Step 0 (Step 0 (Step 0 (Step 0 (error "ambiguous parser?"))))) 
+parse_h (P (T ph _  _) _ _ _)  = fst . eval . ph  (\ a rest -> if eof rest then push a (Step 0 (Step 0 (Step 0 (Step 0 (Step 0 (error "ambiguous parser?"))))) )
                                                                            else error "pEnd missing?") 
 
 -- | The data type `Steps` is the core data type around which the parsers are constructed.
@@ -451,7 +452,7 @@
 eval :: Steps   a      ->  a
 eval (Step  n    l)     =   {- trace ("Step " ++ show n ++ "\n")-} (eval l)
 eval (Micro  _    l)    =   eval l
-eval (Fail   ss  ls  )  =   trace' ("expecting: " ++ show ss) (eval (getCheapest 3 (map ($ss) ls))) 
+eval (Fail   ss  ls  )  =   trace' ("expecting: " ++ show ss) (eval (getCheapest 5 (map ($ss) ls))) 
 eval (Apply  f   l   )  =   f (eval l)
 eval (End_f   _  _   )  =   error "dangling End_f constructor"
 eval (End_h   _  _   )  =   error "dangling End_h constructor"
diff --git a/uu-parsinglib.cabal b/uu-parsinglib.cabal
--- a/uu-parsinglib.cabal
+++ b/uu-parsinglib.cabal
@@ -1,5 +1,5 @@
 Name:                uu-parsinglib
-Version:             2.7.3
+Version:             2.7.3.1
 Build-Type:          Simple
 License:             MIT
 Copyright:           S Doaitse Swierstra