diff --git a/Text/TeXMath/Parser.hs b/Text/TeXMath/Parser.hs
--- a/Text/TeXMath/Parser.hs
+++ b/Text/TeXMath/Parser.hs
@@ -433,11 +433,22 @@
 
 texSymbol :: TP Exp
 texSymbol = try $ do
+  negated <- (symbol "\\not" >> return True) <|> return False
   sym <- operator <|> command
   case M.lookup sym symbols of
-       Just s   -> return s
+       Just s   -> if negated then neg s else return s
        Nothing  -> pzero
 
+neg :: Exp -> TP Exp
+neg (ESymbol Rel x) = ESymbol Rel `fmap`
+  case x of
+       "\x2282" -> return "\x2284"
+       "\x2283" -> return "\x2285"
+       "\x2286" -> return "\x2288"
+       "\x2287" -> return "\x2289"
+       _        -> pzero
+neg _ = pzero
+
 -- The lexer
 lexer :: P.TokenParser st
 lexer = P.makeTokenParser texMathDef
@@ -637,6 +648,10 @@
            , ("\\supset", ESymbol Rel "\x2283")
            , ("\\subseteq", ESymbol Rel "\x2286")
            , ("\\supseteq", ESymbol Rel "\x2287")
+           , ("\\nsubset", ESymbol Rel "\x2284")
+           , ("\\nsupset", ESymbol Rel "\x2285")
+           , ("\\nsubseteq", ESymbol Rel "\x2288")
+           , ("\\nsupseteq", ESymbol Rel "\x2289")
            , ("\\sqsubset", ESymbol Rel "\x228F")
            , ("\\sqsupset", ESymbol Rel "\x2290")
            , ("\\sqsubseteq", ESymbol Rel "\x2291")
diff --git a/texmath.cabal b/texmath.cabal
--- a/texmath.cabal
+++ b/texmath.cabal
@@ -1,5 +1,5 @@
 Name:                texmath
-Version:             0.6.5
+Version:             0.6.5.1
 Cabal-Version:       >= 1.6
 Build-type:          Custom
 Synopsis:            Conversion of LaTeX math formulas to MathML or OMML.