--- modules/number/number.module
+++ modules/number/number.module
@@ -565,6 +564,14 @@ function number_decimal_validate($elemen
     else {
       $value = str_replace($element['#decimal'], '.', $value);
       $value = round($value, $element['#scale']);
+      
+      list($units, $fraction) = explode('.', $value);
+      if (is_null($fraction)) {
+        $fraction = '';
+      }
+      $fraction = str_pad($fraction, $element['#scale'], '0');
+      $value = $units . '.' . $fraction;
+      
       form_set_value($element[$field_key], $value, $form_state);
     }
   }