diff --git a/library/HTMLPurifier/UnitConverter.php b/library/HTMLPurifier/UnitConverter.php
index 166f3bf30..b5a1eab5c 100644
--- a/library/HTMLPurifier/UnitConverter.php
+++ b/library/HTMLPurifier/UnitConverter.php
@@ -261,7 +261,7 @@ private function div($s1, $s2, $scale)
      */
     private function round($n, $sigfigs)
     {
-        $new_log = (int)floor(log(abs($n), 10)); // Number of digits left of decimal - 1
+        $new_log = (int)floor(log(abs((float)$n), 10)); // Number of digits left of decimal - 1
         $rp = $sigfigs - $new_log - 1; // Number of decimal places needed
         $neg = $n < 0 ? '-' : ''; // Negative sign
         if ($this->bcmath) {
@@ -276,7 +276,7 @@ private function round($n, $sigfigs)
             }
             return $n;
         } else {
-            return $this->scale(round($n, $sigfigs - $new_log - 1), $rp + 1);
+            return $this->scale(round((float)$n, $sigfigs - $new_log - 1), $rp + 1);
         }
     }
 
@@ -300,7 +300,7 @@ private function scale($r, $scale)
             // Now we return it, truncating the zero that was rounded off.
             return substr($precise, 0, -1) . str_repeat('0', -$scale + 1);
         }
-        return sprintf('%.' . $scale . 'f', (float)$r);
+        return number_format((float)$r, $scale, '.', '');
     }
 }
 
diff --git a/tests/HTMLPurifier/UnitConverterTest.php b/tests/HTMLPurifier/UnitConverterTest.php
index 53543f023..7c7472e08 100644
--- a/tests/HTMLPurifier/UnitConverterTest.php
+++ b/tests/HTMLPurifier/UnitConverterTest.php
@@ -101,6 +101,13 @@ public function testRoundingUserPrecision()
         $this->assertConversion('111.12pt', '1.5433in');
         $this->assertConversion('11.112pt', '0.15433in');
     }
+    
+    public function testDecimalSeparatorComma()
+    {
+        setlocale(LC_ALL, 'de_DE@euro', 'de_DE', 'deu_deu');
+        $this->assertConversion('11.11px', '0.294cm');
+        setlocale(LC_ALL, '');
+    }
 
     public function testRoundingBigNumber()
     {