diff --git a/path.cabal b/path.cabal
--- a/path.cabal
+++ b/path.cabal
@@ -1,5 +1,5 @@
 name:                path
-version:             0.3.0
+version:             0.4.0
 synopsis:            Path
 description:         Path
 license:             BSD3
@@ -29,3 +29,7 @@
                  , hspec
                  , mtl
                  , path
+
+source-repository head
+    type:     git
+    location: https://github.com/chrisdone/path.git
diff --git a/src/Path.hs b/src/Path.hs
--- a/src/Path.hs
+++ b/src/Path.hs
@@ -65,6 +65,7 @@
   | InvalidRelDir FilePath
   | InvalidAbsFile FilePath
   | InvalidRelFile FilePath
+  | Couldn'tStripPrefixDir FilePath FilePath
   deriving (Show,Typeable)
 instance Exception PathParseException
 
@@ -81,7 +82,10 @@
 parseAbsDir filepath =
   if FilePath.isAbsolute filepath &&
      not (null (normalizeDir filepath)) &&
-     not (isPrefixOf "~/" filepath)
+     not (isPrefixOf "~/" filepath) &&
+     not (isSuffixOf "/.." filepath) &&
+     not (isInfixOf "/../" filepath) &&
+     not (isPrefixOf "../" filepath)
      then return (Path (normalizeDir filepath))
      else throwM (InvalidAbsDir filepath)
 
@@ -96,7 +100,11 @@
   if not (FilePath.isAbsolute filepath) &&
      not (null filepath) &&
      not (isPrefixOf "~/" filepath) &&
-     not (null (normalizeDir filepath))
+     not (isPrefixOf "../" filepath) &&
+     not (isSuffixOf "/.." filepath) &&
+     not (isInfixOf "/../" filepath) &&
+     not (null (normalizeDir filepath)) &&
+     filepath /= ".."
      then return (Path (normalizeDir filepath))
      else throwM (InvalidRelDir filepath)
 
@@ -110,7 +118,11 @@
   if FilePath.isAbsolute filepath &&
      not (FilePath.hasTrailingPathSeparator filepath) &&
      not (isPrefixOf "~/" filepath) &&
-     not (null (normalizeFile filepath))
+     not (isPrefixOf "../" filepath) &&
+     not (isSuffixOf "/.." filepath) &&
+     not (isInfixOf "/../" filepath) &&
+     not (null (normalizeFile filepath)) &&
+     filepath /= ".."
      then return (Path (normalizeFile filepath))
      else throwM (InvalidAbsFile filepath)
 
@@ -121,10 +133,16 @@
 parseRelFile :: MonadThrow m
              => FilePath -> m (Path Rel File)
 parseRelFile filepath =
-  if not (FilePath.isAbsolute filepath || FilePath.hasTrailingPathSeparator filepath) &&
+  if not (FilePath.isAbsolute filepath ||
+          FilePath.hasTrailingPathSeparator filepath) &&
      not (null filepath) &&
      not (isPrefixOf "~/" filepath) &&
-     not (null (normalizeFile filepath))
+     not (isPrefixOf "../" filepath) &&
+     not (isInfixOf "/../" filepath) &&
+     not (isSuffixOf "/.." filepath) &&
+     not (isInfixOf "/../" filepath) &&
+     not (null (normalizeFile filepath)) &&
+     filepath /= ".."
      then return (Path (normalizeFile filepath))
      else throwM (InvalidRelFile filepath)
 
@@ -217,13 +235,18 @@
 --
 -- @stripDir (a :: Path Abs …) (b :: Path Rel …)@
 --
--- @stripDir (a :: Path Rel) (b :: Path Abs …)@
+-- @stripDir (a :: Path Rel …) (b :: Path Abs …)@
 --
 -- In other words the bases must match.
 --
-stripDir :: Path b Dir -> Path b t -> Maybe (Path Rel t)
+-- Throws: 'Couldn'tStripPrefixDir'
+--
+stripDir :: MonadThrow m
+         => Path b Dir -> Path b t -> m (Path Rel t)
 stripDir (Path p) (Path l) =
-  fmap Path (stripPrefix p l)
+  case fmap Path (stripPrefix p l) of
+    Nothing -> throwM (Couldn'tStripPrefixDir p l)
+    Just ok -> return ok
 
 -- | Is p a parent of the given location? Implemented in terms of
 -- 'stripDir'. The bases must match.
diff --git a/test/Main.hs b/test/Main.hs
--- a/test/Main.hs
+++ b/test/Main.hs
@@ -4,6 +4,9 @@
 
 module Main where
 
+import Control.Applicative
+import Control.Monad
+import Data.Maybe
 import Data.Monoid
 import Path
 import Path.Internal
@@ -25,6 +28,25 @@
      describe "Operations: isParentOf" operationIsParentOf
      describe "Operations: parent" operationParent
      describe "Operations: filename" operationFilename
+     describe "Restrictions" restrictions
+
+-- | Restricting the input of any tricks.
+restrictions :: Spec
+restrictions =
+  do parseFails "~/"
+     parseFails "~/foo"
+     parseFails "~/foo/bar"
+     parseFails "../"
+     parseFails ".."
+     parseFails "/.."
+     parseFails "/foo/../bar/"
+     parseFails "/foo/bar/.."
+  where parseFails x =
+          it (show x ++ " should be rejected")
+             (isNothing (void (parseAbsDir x) <|>
+                         void (parseRelDir x) <|>
+                         void (parseAbsFile x) <|>
+                         void (parseRelDir x)))
 
 -- | The 'filename' operation.
 operationFilename :: Spec