diff --git a/README.md b/README.md
index 98e3607..a0415d7 100644
--- a/README.md
+++ b/README.md
@@ -25,8 +25,9 @@ sure everything is working as intented.
 
 ### Argument Handling
 
-The API for helping defing flexible function signatures consists of two helper
-functions and two types: `arg_read`, `arg_write`, `ArgRead` and `ArgWrite`.
+The API for helping defing flexible function signatures consists of two types
+and four helper functions: `ArgRead` and `ArgWrite`; `arg_read`, `arg_write`,
+`arg_isdir` and `arg_mkdir`.
 
 <!-- BEGIN: copied from inline doc strings -->
 
@@ -35,7 +36,6 @@ functions and two types: `arg_read`, `arg_write`, `ArgRead` and `ArgWrite`.
 ```jl
 ArgRead = Union{AbstractString, AbstractCmd, IO}
 ```
-
 The `ArgRead` types is a union of the types that the `arg_read` function knows
 how to convert into readable IO handles. See [`arg_read`](@ref) for details.
 
@@ -44,7 +44,6 @@ how to convert into readable IO handles. See [`arg_read`](@ref) for details.
 ```jl
 ArgWrite = Union{AbstractString, AbstractCmd, IO}
 ```
-
 The `ArgWrite` types is a union of the types that the `arg_write` function knows
 how to convert into writeable IO handles, except for `Nothing` which `arg_write`
 handles by generating a temporary file. See [`arg_write`](@ref) for details.
@@ -54,7 +53,6 @@ handles by generating a temporary file. See [`arg_write`](@ref) for details.
 ```jl
 arg_read(f::Function, arg::ArgRead) -> f(arg_io)
 ```
-
 The `arg_read` function accepts an argument `arg` that can be any of these:
 
 - `AbstractString`: a file path to be opened for reading
@@ -71,7 +69,6 @@ flushed but not closed before returning from `arg_read`.
 arg_write(f::Function, arg::ArgWrite) -> arg
 arg_write(f::Function, arg::Nothing) -> tempname()
 ```
-
 The `arg_write` function accepts an argument `arg` that can be any of these:
 
 - `AbstractString`: a file path to be opened for writing
@@ -90,6 +87,33 @@ If there is an error during the evaluation of the body, a path that is opened by
 `arg_write` for writing will be deleted, whether it's passed in as a string or a
 temporary path generated when `arg` is `nothing`.
 
+#### arg_isdir
+
+```jl
+arg_isdir(f::Function, arg::AbstractString) -> f(arg)
+```
+The `arg_isdir` function takes `arg` which must be the path to an existing
+directory (an error is raised otherwise) and passes that path to `f` finally
+returning the result of `f(arg)`. This is definitely the least useful tool
+offered by `ArgTools` and mostly exists for symmetry with `arg_mkdir` and to
+give consistent error messages.
+
+#### arg_mkdir
+
+```jl
+arg_mkdir(f::Function, arg::AbstractString) -> arg
+arg_mkdir(f::Function, arg::Nothing) -> mktempdir()
+```
+The `arg_mkdir` function takes `arg` which must either be one of:
+
+- a path to an already existing empty directory,
+- a non-existent path which can be created as a directory, or
+- `nothing` in which case a temporary directory is created.
+
+In all cases the path to the directory is returned. If an error occurs during
+`f(arg)`, the directory is returned to its original state: if it already existed
+but was empty, it will be emptied; if it did not exist it will be deleted.
+
 <!-- END: copied from inline doc strings -->
 
 ### Function Testing
diff --git a/src/ArgTools.jl b/src/ArgTools.jl
index 776df32..0765f7d 100644
--- a/src/ArgTools.jl
+++ b/src/ArgTools.jl
@@ -98,32 +98,62 @@ function arg_write(f::Function, arg::IO)
     return arg
 end
 
+"""
+    arg_isdir(f::Function, arg::AbstractString) -> f(arg)
+
+The `arg_isdir` function takes `arg` which must be the path to an existing
+directory (an error is raised otherwise) and passes that path to `f` finally
+returning the result of `f(arg)`. This is definitely the least useful tool
+offered by `ArgTools` and mostly exists for symmetry with `arg_mkdir` and to
+give consistent error messages.
+"""
 function arg_isdir(f::Function, arg::AbstractString)
     isdir(arg) || error("arg_isdir: $(repr(arg)) not a directory")
     return f(arg)
 end
 
+"""
+    arg_mkdir(f::Function, arg::AbstractString) -> arg
+    arg_mkdir(f::Function, arg::Nothing) -> mktempdir()
+
+The `arg_mkdir` function takes `arg` which must either be one of:
+
+- a path to an already existing empty directory,
+- a non-existent path which can be created as a directory, or
+- `nothing` in which case a temporary directory is created.
+
+In all cases the path to the directory is returned. If an error occurs during
+`f(arg)`, the directory is returned to its original state: if it already existed
+but was empty, it will be emptied; if it did not exist it will be deleted.
+"""
 function arg_mkdir(f::Function, arg::Union{AbstractString, Nothing})
-    restore = false
+    existed = false
     if arg === nothing
         arg = mktempdir()
     else
         st = stat(arg)
-        if !ispath(arg)
+        if !ispath(st)
             mkdir(arg)
-        elseif !isdir(arg)
+        elseif !isdir(st)
             error("arg_mkdir: $(repr(arg)) not a directory")
         else
             isempty(readdir(arg)) ||
                 error("arg_mkdir: $(repr(arg)) directory not empty")
-            restore = true
+            existed = true
         end
     end
     try f(arg)
     catch
-        chmod(arg, 0o700, recursive=true)
-        rm(arg, force=true, recursive=true)
-        restore && mkdir(arg)
+        if existed
+            for name in readdir(arg)
+                path = joinpath(arg, name)
+                chmod(path, 0o700, recursive=true)
+                rm(path, force=true, recursive=true)
+            end
+        else
+            chmod(arg, 0o700, recursive=true)
+            rm(arg, force=true, recursive=true)
+        end
         rethrow()
     end
     return arg
diff --git a/test/runtests.jl b/test/runtests.jl
index 4b0b9b5..dd3105d 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -107,19 +107,26 @@ end
 
     @testset "arg_mkdir" begin
         dir = tempname()
+        # creates a non-existent directory
         @test dir == arg_mkdir(d -> "%$d%", dir)
         @test isdir(dir)
+        # accepts a pre-existing empty directory
         @test dir == arg_mkdir(d -> "%$d%", dir)
+        @test isdir(dir)
+        # refuses a non-empty directory
         touch(joinpath(dir, "file"))
         @test_throws ErrorException arg_mkdir(identity, dir)
         rm(dir, recursive=true)
+        # refuses a non-directory
         file = tempname()
         touch(file)
         @test_throws ErrorException arg_mkdir(identity, file)
         rm(file)
+        # creates a temporary directory
         dir = arg_mkdir(d -> "%$d%", nothing)
         @test isdir(dir)
         rm(dir)
+        # on error, restores (deletes) a non-existent directory
         tmp = tempname()
         @test_throws ErrorException arg_mkdir(tmp) do dir
             @test dir == tmp
@@ -129,5 +136,21 @@ end
             error("boof")
         end
         @test !ispath(tmp)
+        # on error, restores (empties) an empty directory
+        mkdir(tmp)
+        chmod(tmp, 0o741)
+        st = stat(tmp)
+        file = joinpath(tmp, "file")
+        @test_throws ErrorException arg_mkdir(tmp) do dir
+            @test dir == tmp
+            touch(file)
+            chmod(file, 0o000)
+            error("blammo")
+        end
+        @test !ispath(file)
+        @test isdir(tmp)
+        @test isempty(readdir(tmp))
+        @test filemode(tmp) == filemode(st)
+        @test Base.Filesystem.samefile(st, stat(tmp))
     end
 end