diff --git a/lib/Quox/Parser/FromParser/Error.idr b/lib/Quox/Parser/FromParser/Error.idr
index d561df7..301ff59 100644
--- a/lib/Quox/Parser/FromParser/Error.idr
+++ b/lib/Quox/Parser/FromParser/Error.idr
@@ -39,12 +39,14 @@ data Error =
 export
 prettyLexError : {opts : _} -> String -> LexError -> Eff Pretty (Doc opts)
 prettyLexError file (Err reason line col char) = do
-  let loc = makeLoc file (MkBounds line col line col)
   reason <- case reason of
-    EndInput    => pure "unexpected end of input"
-    NoRuleApply => pure $ text "unrecognised character: \{show char}"
+    Other msg => pure $ text msg
+    NoRuleApply => case char of
+      Just char => pure $ text "unrecognised character: \{show char}"
+      Nothing   => pure $ text "unexpected end of input"
     ComposeNotClosing (sl, sc) (el, ec) => pure $
       hsep ["unterminated token at", !(prettyBounds (MkBounds sl sc el ec))]
+  let loc = makeLoc file (MkBounds line col line col)
   pure $ vappend !(prettyLoc loc) reason
 
 export
diff --git a/lib/Quox/Parser/Lexer.idr b/lib/Quox/Parser/Lexer.idr
index 57b7e96..eb71ad9 100644
--- a/lib/Quox/Parser/Lexer.idr
+++ b/lib/Quox/Parser/Lexer.idr
@@ -34,16 +34,27 @@ data Token =
   | Sup Nat
 %runElab derive "Token" [Eq, Ord, Show]
 
--- token or whitespace
+||| token or whitespace
+||| @ Skip whitespace, comments, etc
+||| @ Invalid a token which failed a post-lexer check
+|||           (e.g. a qualified name containing a keyword)
+||| @ T a well formed token
 public export
-0 TokenW : Type
-TokenW = Maybe Token
+data ExtToken = Skip | Invalid String String | T Token
+%runElab derive "ExtToken" [Eq, Ord, Show]
 
 
+public export
+data ErrorReason =
+    NoRuleApply
+  | ComposeNotClosing (Int, Int) (Int, Int)
+  | Other String
+%runElab derive "ErrorReason" [Eq, Ord, Show]
+
 public export
 record Error where
   constructor Err
-  reason    : StopReason
+  reason    : ErrorReason
   line, col : Int
   ||| `Nothing` if the error is at the end of the input
   char      : Maybe Char
@@ -52,19 +63,14 @@ record Error where
 
 
 private
-skip : Lexer -> Tokenizer TokenW
-skip t = match t $ const Nothing
+skip : Lexer -> Tokenizer ExtToken
+skip t = match t $ const Skip
 
 private
-match : Lexer -> (String -> Token) -> Tokenizer TokenW
-match t f = Tokenizer.match t (Just . f)
-%hide Tokenizer.match
+tmatch : Lexer -> (String -> Token) -> Tokenizer ExtToken
+tmatch t f = match t (T . f)
 
 
-private
-name : Tokenizer TokenW
-name = match name $ Name . fromListP . split (== '.') . normalizeNfc
-
 ||| [todo] escapes other than `\"` and (accidentally) `\\`
 export
 fromStringLit : String -> String
@@ -76,17 +82,17 @@ fromStringLit = pack . go . unpack . drop 1 . dropLast 1 where
   go (c :: cs)         = c :: go cs
 
 private
-string : Tokenizer TokenW
-string = match stringLit (Str . fromStringLit)
+string : Tokenizer ExtToken
+string = tmatch stringLit (Str . fromStringLit)
 
 private
-nat : Tokenizer TokenW
-nat = match (some (range '0' '9')) (Nat . cast)
+nat : Tokenizer ExtToken
+nat = tmatch (some (range '0' '9')) (Nat . cast)
 
 private
-tag : Tokenizer TokenW
-tag = match (is '\'' <+> name)      (Tag . drop 1)
-  <|> match (is '\'' <+> stringLit) (Tag . fromStringLit . drop 1)
+tag : Tokenizer ExtToken
+tag = tmatch (is '\'' <+> name)      (Tag . drop 1)
+  <|> tmatch (is '\'' <+> stringLit) (Tag . fromStringLit . drop 1)
 
 
 
@@ -112,17 +118,17 @@ supToNat = cast . pack . map fromSup . unpack
 
 -- ★0, Type0. base ★/Type is a Reserved
 private
-universe : Tokenizer TokenW
+universe : Tokenizer ExtToken
 universe = universeWith "★" <|> universeWith "Type" where
-  universeWith : String -> Tokenizer TokenW
+  universeWith : String -> Tokenizer ExtToken
   universeWith pfx =
     let len = length pfx in
-    match (exact pfx <+> digits) (TYPE . cast . drop len)
+    tmatch (exact pfx <+> digits) (TYPE . cast . drop len)
 
 private
-sup : Tokenizer TokenW
-sup = match (some $ pred isSupDigit) (Sup . supToNat)
-  <|> match (is '^' <+> digits)      (Sup . cast . drop 1)
+sup : Tokenizer ExtToken
+sup = tmatch (some $ pred isSupDigit) (Sup . supToNat)
+  <|> tmatch (is '^' <+> digits)      (Sup . cast . drop 1)
 
 
 private %inline
@@ -165,17 +171,23 @@ resString : Reserved -> String
 resString (Only r)   = resString1 r
 resString (r `Or` _) = resString1 r
 
+||| return both representative strings for a token description
+public export
+resString2 : Reserved -> List String
+resString2 (Only r)   = [resString1 r]
+resString2 (r `Or` s) = [resString1 r, resString1 s]
+
 private
-resTokenizer1 : Reserved1 -> String -> Tokenizer TokenW
+resTokenizer1 : Reserved1 -> String -> Tokenizer ExtToken
 resTokenizer1 r str =
   let res : String -> Token := const $ Reserved str in
-  case r of Word w => match (exact w <+> reject idContEnd) res
-            Sym  s => match (exact s <+> reject symCont)   res
-            Punc x => match (exact x)                      res
+  case r of Word w => tmatch (exact w <+> reject idContEnd) res
+            Sym  s => tmatch (exact s <+> reject symCont)   res
+            Punc x => tmatch (exact x)                      res
 
 ||| match a reserved token
 export
-resTokenizer : Reserved -> Tokenizer TokenW
+resTokenizer : Reserved -> Tokenizer ExtToken
 resTokenizer (Only r)   = resTokenizer1 r (resString1 r)
 resTokenizer (r `Or` s) =
   resTokenizer1 r (resString1 r) <|> resTokenizer1 s (resString1 r)
@@ -219,14 +231,31 @@ reserved =
    Word1 "load",
    Word1 "namespace"]
 
+public export
+reservedStrings : List String
+reservedStrings = map resString reserved
+
+public export
+allReservedStrings : List String
+allReservedStrings = foldMap resString2 reserved
+
 ||| `IsReserved str` is true if `Reserved str` might actually show up in
 ||| the token stream
 public export
 IsReserved : String -> Type
-IsReserved str = str `Elem` map resString reserved
+IsReserved str = So (str `elem` allReservedStrings)
+
+private
+name : Tokenizer ExtToken
+name =
+  match name $ \str =>
+    let parts = split (== '.') $ normalizeNfc str in
+    case find (`elem` allReservedStrings) (toList parts) of
+      Nothing => T $ Name $ fromListP parts
+      Just w  => Invalid "reserved word '\{w}' inside name \{str}" str
 
 export
-tokens : Tokenizer TokenW
+tokens : Tokenizer ExtToken
 tokens = choice $
   map skip [pred isWhitespace,
             lineComment (exact "--" <+> reject symCont),
@@ -235,10 +264,24 @@ tokens = choice $
   map resTokenizer reserved <+>
   [sup, nat, string, tag, name]
 
+export
+check : Alternative f =>
+        WithBounds ExtToken -> Either Error (f (WithBounds Token))
+check (MkBounded val irr bounds@(MkBounds line col _ _)) = case val of
+  Skip            => Right empty
+  T tok           => Right $ pure $ MkBounded tok irr bounds
+  Invalid msg tok => Left  $ Err (Other msg) line col (index 0 tok)
+
+export
+toErrorReason : StopReason -> Maybe ErrorReason
+toErrorReason EndInput                = Nothing
+toErrorReason NoRuleApply             = Just NoRuleApply
+toErrorReason (ComposeNotClosing s e) = Just $ ComposeNotClosing s e
+
 export
 lex : String -> Either Error (List (WithBounds Token))
 lex str =
   let (res, reason, line, col, str) = lex tokens str in
-  case reason of
-    EndInput => Right $ mapMaybe sequence res
-    _        => Left  $ Err {reason, line, col, char = index 0 str}
+  case toErrorReason reason of
+    Nothing => concatMap check res @{MonoidApplicative}
+    Just e  => Left $ Err {reason = e, line, col, char = index 0 str}
diff --git a/tests/Tests/Lexer.idr b/tests/Tests/Lexer.idr
index 7823d5d..910a434 100644
--- a/tests/Tests/Lexer.idr
+++ b/tests/Tests/Lexer.idr
@@ -47,7 +47,12 @@ tests = "lexer" :- [
     lexes "    " [],
     lexes "-- line comment" [],
     lexes "name -- line comment" [Name "name"],
-    lexes "-- line comment\nnameBetween -- and another" [Name "nameBetween"],
+    lexes
+      """
+      -- line comment
+      nameBetween -- and another
+      """
+      [Name "nameBetween"],
     lexes "{- block comment -}" [],
     lexes "{- {- nested -} block comment -}" []
   ],
@@ -70,13 +75,14 @@ tests = "lexer" :- [
     lexes "normalïse" [Name "normalïse"],
       -- ↑ replace i + combining ¨ with precomposed ï
     lexes "map#" [Name "map#"],
+    lexes "map#[" [Name "map#", Reserved "["], -- don't actually do this
+    lexes "map #[" [Name "map", Reserved "#["],
     lexes "write!" [Name "write!"],
     lexes "uhh??!?!?!?" [Name "uhh??!?!?!?"],
 
-    todo "check for reserved words in a qname",
-    skip $
-    lexes "abc.fun.def"
-      [Name "abc", Reserved ".", Reserved "λ", Reserved ".", Name "def"],
+    lexFail "abc.fun.ghi",
+    lexFail "abc.λ.ghi",
+    lexFail "abc.ω.ghi",
 
     lexes "+" [Name "+"],
     lexes "*" [Name "*"],