diff --git a/plugin/kcaptcha/kcaptcha.lib.php b/plugin/kcaptcha/kcaptcha.lib.php
index 50a3cef69..fc897b5a1 100644
--- a/plugin/kcaptcha/kcaptcha.lib.php
+++ b/plugin/kcaptcha/kcaptcha.lib.php
@@ -50,13 +50,13 @@ class KCAPTCHA{
             $transparent = (imagecolorat($font, $i, 0) >> 24) == 127;
 
             if(!$reading_symbol && !$transparent){
-                $font_metrics[$alphabet{$symbol}]=array('start'=>$i);
+                $font_metrics[$alphabet[$symbol]]=array('start'=>$i);
                 $reading_symbol=true;
                 continue;
             }
 
             if($reading_symbol && $transparent){
-                $font_metrics[$alphabet{$symbol}]['end']=$i;
+                $font_metrics[$alphabet[$symbol]]['end']=$i;
                 $reading_symbol=false;
                 $symbol++;
                 continue;
@@ -75,7 +75,7 @@ class KCAPTCHA{
         $odd=mt_rand(0,1);
         if($odd==0) $odd=-1;
         for($i=0;$i<$length;$i++){
-            $m=$font_metrics[$this->keystring{$i}];
+            $m=$font_metrics[$this->keystring[$i]];
 
             $y=(($i%2)*$fluctuation_amplitude - $fluctuation_amplitude/2)*$odd
                 + mt_rand(-round($fluctuation_amplitude/3), round($fluctuation_amplitude/3))