diff --git a/README.md b/README.md
index 07f5954..54eb9a7 100644
--- a/README.md
+++ b/README.md
@@ -17,8 +17,6 @@ Supports commit: f68d014bfd4a84a64fb5f6a7c1a83a4162415d4b
 TODO
 ----
 
-- Throw exception on extra chars after keygroup definition
-- Throw exception on key or keygroup overwriting
 - Write better tests.
 - Support Unicode and \b chars.
 
diff --git a/src/toml.php b/src/toml.php
index 10e705c..06faf5e 100755
--- a/src/toml.php
+++ b/src/toml.php
@@ -96,13 +96,19 @@ class Toml
 
                 $keygroup = substr($line, 1, -1);
                 $aKeygroup = explode('.', $keygroup);
+                $last = count($aKeygroup) - 1;
 
-                foreach($aKeygroup as $keygroup)
+                foreach($aKeygroup as $i => $keygroup)
                 {
                     if( !isset($pointer[$keygroup]) )
                     {
                         $pointer[$keygroup] = array();
                     }
+                    elseif($i == $last)
+                    {
+                        // Overwrite key
+                        throw new Exception('Key overwrite previous keys: ' . $line);
+                    }
 
                     // Move pointer forward
                     $pointer = & $pointer[$keygroup];
@@ -112,8 +118,14 @@ class Toml
             elseif(strpos($line, '='))
             {
                 $kv = explode('=', $line, 2);
-
-                $pointer[ trim($kv[0]) ] = self::parseValue( $kv[1] );
+                if(!isset($pointer[ trim($kv[0]) ]))
+                {
+                    $pointer[ trim($kv[0]) ] = self::parseValue( $kv[1] );
+                }
+                else
+                {
+                    throw new Exception('Key overwrite previous keys: ' . $line);
+                }
             }
             elseif($line[0] == '[' && substr($line, -1) != ']')
             {