diff --git a/dblayeroo.php b/dblayeroo.php
index 8523bf2..bdb6219 100644
--- a/dblayeroo.php
+++ b/dblayeroo.php
@@ -1826,17 +1826,28 @@ class dblayeroo
       $operator = "~";
     if ($this->driver === "pgsql" && $operator === "NOT REGEXP")
       $operator = "!~";
-    $hash = md5 ("$field, $operator, $value");
-    $this->whereExpression[] =
-      $this->sep.$this->tableprefix.$this->table.$this->sep.".".
-      $this->sep.$field.$this->sep." ".$operator." :$hash";
-    $this->whereValues[$hash] = array (
-      "field"=>$field,
-      "fieldfull"=> $this->tableprefix.$this->table.".".$field,
-      "operator"=>$operator,
-      "value"=>$value,
-      "hash"=>$hash,
-      "type"=>$this->fieldTypeLight ($field));
+    if ($operator === "IS NULL")
+    {
+      // Operator without parameter
+      $this->whereExpression[] =
+        $this->sep.$this->tableprefix.$this->table.$this->sep.".".
+        $this->sep.$field.$this->sep." ".$operator;
+    }
+    else
+    {
+      // Operator with parameter
+      $hash = md5 ("$field, $operator, $value");
+      $this->whereExpression[] =
+        $this->sep.$this->tableprefix.$this->table.$this->sep.".".
+        $this->sep.$field.$this->sep." ".$operator." :$hash";
+      $this->whereValues[$hash] = array (
+        "field"=>$field,
+        "fieldfull"=> $this->tableprefix.$this->table.".".$field,
+        "operator"=>$operator,
+        "value"=>$value,
+        "hash"=>$hash,
+        "type"=>$this->fieldTypeLight ($field));
+    }
     return $this;
   }
   /* }}} */