diff --git a/pretty.lua b/pretty.lua
index 30e6ac4..e42d52a 100644
--- a/pretty.lua
+++ b/pretty.lua
@@ -237,6 +237,14 @@ local function get_full_function_str (str, start_line, end_line)
     return matched_function
 end
 
+local function width_of_strings_in_l (l, start_i, end_i)
+    local  width = 0
+    for i = start_i or 1, (end_i or #l) do
+        width = width + #l[i]
+    end
+    return width
+end
+
 
 --------------------------------------------------------------------------------
 -- Identifyer stuff
@@ -333,10 +341,11 @@ local function format_key_and_value_string_map (l, key, value, options, depth)
 end
 
 local function format_key_and_value_arbitr_map (l, key, value, options, depth)
+    local index_before_key = #l+1
     l[#l+1] = '['
     format_value(key, options, 'max', l)
     l[#l+1] = ']'
-    l[#l+1] = #l[#l-1] + 2
+    l[#l+1] = width_of_strings_in_l(l, index_before_key)
     l[#l+1] = ' = '
     format_value(value, options, depth, l)
 end
@@ -606,7 +615,7 @@ function format_value (value, options, depth, l)
     if format_func then
         format_func(value, options, depth, l)
     else
-        error(ERROR_UNKNOWN_TYPE:format(type(value), tostring(value)))
+        error(ERROR_UNKNOWN_TYPE:format(type(value), tostring(value)), 2)
     end
 end