diff --git a/analyze_structure.lua b/analyze_structure.lua
index 9b0571a..2aef1e2 100644
--- a/analyze_structure.lua
+++ b/analyze_structure.lua
@@ -191,6 +191,7 @@ end
 --------------------------------------------------------------------------------
 
 local function analyze_structure (root)
+    if type(root) ~= 'table' then  return {}  end
     assert(type(root) == 'table')
 
     local info, visited, next_mark, depth  =  { root = root }, {}, 1, { [root] = 0 }
diff --git a/pretty.lua b/pretty.lua
index 8dc5fa1..733d3ac 100644
--- a/pretty.lua
+++ b/pretty.lua
@@ -394,6 +394,7 @@ end
 
 local function format_string (str, depth, l)
     -- TODO: Add option for escaping unicode characters.
+    -- TODO: Improve cutstring argument.
 
     -- Error checking
     assert( type(str) == 'string' )
@@ -494,41 +495,49 @@ setmetatable(StringBuilder, {
 local DEBUG_OPTIONS = { _all_function_info = true, _table_addr_comment = true }
 
 local KNOWN_OPTIONS = {
-    _table_addr_comment = 'boolean',
-    _all_function_info  = 'boolean',
-    cut_strings         = 'boolean',
-    include_closure     = 'boolean',
-    indent              = 'string',
-    math_shorthand      = 'boolean',
-    max_depth           = 'number',
-    more_function_info  = 'boolean',
-    recursion           = 'string',
-    short_builtins      = 'boolean',
+    _table_addr_comment = { type = 'boolean', default = false },
+    _all_function_info  = { type = 'boolean', default = false },
+    cut_strings         = { type = 'boolean', default = false },
+    include_closure     = { type = 'boolean', default = false },
+    indent              = { type = 'string',  default = '\t' }, -- TODO: Change default to '    '.
+    math_shorthand      = { type = 'boolean', default = false },
+    max_depth           = { type = 'number',  default = math.huge },
+    more_function_info  = { type = 'boolean', default = false },
+    recursion           = { type = 'string',  default = 'ignore', accepted = {['ignore'] = true, ['marked'] = true} },
+    short_builtins      = { type = 'boolean', default = false },
 }
 
 local function ensure_that_all_options_are_known (options)
     assert(type(options) == 'table')
+    -- Error check options
     for option_name, option_value in pairs(options) do
         if not KNOWN_OPTIONS[option_name] then
             error(('[pretty]: Unknown option: %s. Was given value %s (%s)'):format(option_name, option_value, type(option_value)), 2)
-        elseif type(option_value) ~= KNOWN_OPTIONS[option_name] then
-            error(('[pretty]: Bad value given to option %s: %s (%s). Expected value of type %s'):format(option_name, option_value, type(option_value), KNOWN_OPTIONS[option_name]), 2)
+        elseif type(option_value) ~= KNOWN_OPTIONS[option_name].type then
+            error(('[pretty]: Bad value given to option %s: %s (%s). Expected value of type %s'):format(option_name, option_value, type(option_value), KNOWN_OPTIONS[option_name].type), 2)
+        elseif KNOWN_OPTIONS[option_name].accepted and not KNOWN_OPTIONS[option_name].accepted[option_value] then
+            error(('[pretty]: Bad value given to option %s: %s (%s). Expected one of: %s'):format(option_name, option_value, type(option_value), table.concat(KNOWN_OPTIONS[option_name].accepted, ', ')), 2)
         end
     end
+    -- Assign default values
+    for option_name, option_info in pairs(KNOWN_OPTIONS) do
+        if not options[option_name] then
+            options[option_name] = option_info.default
+        end
+    end
+    -- Returns options
+    return options
 end
 
 local function pretty_format (value, options)
     -- Error checking
-    options = options or {}
-    options.max_depth = options.max_depth or math.huge
-    options.indent    = options.indent    or '\t'
-    ensure_that_all_options_are_known(options)
+    local options  =  ensure_that_all_options_are_known(options or {})
 
     -- Setup StringBuilder
     local l = StringBuilder()
           l.visited = { next_mark = 1 }
           l.options = options
-          l.info = (type(value) == 'table') and analyze_structure(value) or {}
+          l.info    = analyze_structure(value)
 
     -- Format value.
     format_value(value, 0, l)
diff --git a/test/test_resilience.lua b/test/test_resilience.lua
index f3beb04..900684e 100644
--- a/test/test_resilience.lua
+++ b/test/test_resilience.lua
@@ -41,6 +41,11 @@ SUITE:addTest('Dont allow bad types in options', function ()
     assert(error_msg)
 end)
 
+SUITE:addTest('Dont allow bad values in recursion', function ()
+    local error_msg = bad_call(pretty, 'Hello World', { recursion = "hello world" })
+    assert(error_msg)
+end)
+
 --------------------------------------------------------------------------------
 -- Survive not loading libs