diff --git a/program/lib/Roundcube/rcube_text2html.php b/program/lib/Roundcube/rcube_text2html.php
index cb4390e5d..60016fffd 100644
--- a/program/lib/Roundcube/rcube_text2html.php
+++ b/program/lib/Roundcube/rcube_text2html.php
@@ -163,7 +163,7 @@ class rcube_text2html
         // find/mark quoted lines...
         for ($n=0, $cnt=count($text); $n < $cnt; $n++) {
             $flowed = false;
-            if ($this->config['flowed'] && ord($text[0]) == $flowed_char) {
+            if ($this->config['flowed'] && ord($text[$n][0]) == $flowed_char) {
                 $flowed   = true;
                 $text[$n] = substr($text[$n], 1);
             }
@@ -259,17 +259,24 @@ class rcube_text2html
 
         // replace spaces with non-breaking spaces
         if ($is_flowed) {
-            $text = preg_replace_callback('/(^|[^ ])( +)/', function($matches) {
-                    if (!strlen($matches[2])) {
-                        return str_repeat($nbsp, strlen($matches[2]));
-                    }
-                    else {
-                        return $matches[1] . ' ' . str_repeat($nbsp, strlen($matches[2])-1);
-                    }
-                }, $text);
+            $pos  = 0;
+            $diff = 0;
+            $len  = strlen($nbsp);
+            $copy = $text;
+
+            while (($pos = strpos($text, ' ', $pos)) !== false) {
+                if ($pos == 0 || $text[$pos-1] == ' ') {
+                    $copy = substr_replace($copy, $nbsp, $pos + $diff, 1);
+                    $diff += $len - 1;
+                }
+                $pos++;
+            }
+
+            $text = $copy;
         }
         else {
-            $text = str_replace(' ', $nbsp, $text);
+            // make the whole line non-breakable
+            $text = str_replace(array(' ', '-'), array($nbsp, '-&#8288;'), $text);
         }
 
         return $text;