diff --git a/Tests/ipaddressesTest.php b/Tests/ipaddressesTest.php
index 1603092..d72fded 100644
--- a/Tests/ipaddressesTest.php
+++ b/Tests/ipaddressesTest.php
@@ -355,13 +355,13 @@ class ipaddressesTest extends PHPUnit_Framework_TestCase
   {
     $i = new ipaddresses ();
     $res = $i->netmask2cidr ("127.0.0.0");
-    $this->assertSame (7, $res);
+    $this->assertSame (false, $res);
   }
   public function test_netmask2cidr7 ()
   {
     $i = new ipaddresses ();
     $res = $i->netmask2cidr ("63.0.0.0");
-    $this->assertSame (6, $res);
+    $this->assertSame (false, $res);
   }
   public function test_netmask2cidr8 ()
   {
@@ -369,6 +369,12 @@ class ipaddressesTest extends PHPUnit_Framework_TestCase
     $res = $i->netmask2cidr ("155.0.0.0");
     $this->assertSame (false, $res);
   }
+  public function test_netmask2cidr9 ()
+  {
+    $i = new ipaddresses ();
+    $res = $i->netmask2cidr ("0.0.0.255");
+    $this->assertSame (false, $res);
+  }
 
   public function test_netmask2cidrWildcard_1 ()
   {
diff --git a/ipaddresses.php b/ipaddresses.php
index 5456fa0..c6ca209 100644
--- a/ipaddresses.php
+++ b/ipaddresses.php
@@ -494,14 +494,14 @@ class ipaddresses
     if ($netmask === FALSE)
       throw new \Exception (dgettext ("domframework", "Invalid netmask"), 500);
     $netmask = decbin ($netmask);
+    $netmask = sprintf ("%032s", $netmask);
     $res = -1;
     for ($i = 0 ; $i < 32 ; $i++)
     {
-      if (! isset ($netmask[$i]))
+      if ($res === -1 && $netmask[$i] === $maskdirect)
       {
-        break;
       }
-      elseif ($res == -1 && $netmask[$i] === $maskrevert)
+      elseif ($res === -1 && $netmask[$i] === $maskrevert)
       {
         $res = $i;
       }
@@ -509,6 +509,9 @@ class ipaddresses
       {
         return false;
       }
+      else
+      {
+      }
     }
     if ($res === -1 && $i === 32)
       return 32;