diff --git a/NEW_FEATURES.txt b/NEW_FEATURES.txt
index cc126c5a..ce09a56f 100644
--- a/NEW_FEATURES.txt
+++ b/NEW_FEATURES.txt
@@ -50,6 +50,15 @@ Smarty 3.1.22
    the setting of $static_classes will be checked.
    Note: That this security check is performed at compile time.
 
+    - trusted constants .
+   The Smarty_Security class has the new property $trusted_constants to restrict access to constants.
+   It's an array of trusted constant names.
+         Format:
+         array (
+                    'SMARTY_DIR' , // allowed constant
+                }
+   If the array is empty (default) the usage of constants  can be controlled with the
+   Smarty_Security::$allow_constants property (default true)
 
 
 
diff --git a/change_log.txt b/change_log.txt
index 2e770538..5a937a27 100644
--- a/change_log.txt
+++ b/change_log.txt
@@ -1,8 +1,8 @@
  ===== 3.1.22-dev ===== (xx.xx.2015)
- 23.03.2015
- - bugfix problems when {function}{/function} defined a template function in a cached subtemplate and it was called {call} 
-          from a not cached subtemplate {forum topic 25468}
-          
+ 27.03.2015
+  - bugfix Smarty_Security->allow_constants=false; did also disable true, false and null (change of 16.03.2015)
+  - improvement added a whitelist for trusted constants to security Smarty_Security::$trusted_constants (forum topic 25471)
+
  20.03.2015
   - bugfix make sure that function properties get saved only in compiled files containing the fuction definition {forum topic 25452}
   - bugfix correct update of global variable values on exit of template functions. (reported under Smarty Developers)
diff --git a/lexer/smarty_internal_templateparser.y b/lexer/smarty_internal_templateparser.y
index 6ea97782..956d5321 100644
--- a/lexer/smarty_internal_templateparser.y
+++ b/lexer/smarty_internal_templateparser.y
@@ -486,8 +486,8 @@ smartytag(res)   ::= LDEL varindexed(vi) EQUAL expr(e) attributes(a). {
                   // tag with optional Smarty2 style attributes
 smartytag(res)   ::= LDEL ID(i) attributes(a). {
         if (defined(i)) {
-            if (isset($this->smarty->security_policy) && !$this->smarty->security_policy->allow_constants) {
-                 $this->compiler->trigger_template_error("Security: access to constants not permitted");
+            if (isset($this->smarty->security_policy)) {
+                $this->smarty->security_policy->isTrustedConstant(i, $this->compiler);
             }
             res = $this->compiler->compileTag('private_print_expression',a,array('value'=>i));
         } else {
@@ -496,8 +496,8 @@ smartytag(res)   ::= LDEL ID(i) attributes(a). {
 }
 smartytag(res)   ::= LDEL ID(i). {
         if (defined(i)) {
-            if (isset($this->smarty->security_policy) && !$this->smarty->security_policy->allow_constants) {
-                 $this->compiler->trigger_template_error("Security: access to constants not permitted");
+            if (isset($this->smarty->security_policy)) {
+                $this->smarty->security_policy->isTrustedConstant(i, $this->compiler);
             }
             res = $this->compiler->compileTag('private_print_expression',array(),array('value'=>i));
         } else {
@@ -509,8 +509,8 @@ smartytag(res)   ::= LDEL ID(i). {
                   // tag with modifier and optional Smarty2 style attributes
 smartytag(res)   ::= LDEL ID(i) modifierlist(l)attributes(a). {
         if (defined(i)) {
-            if (isset($this->smarty->security_policy) && !$this->smarty->security_policy->allow_constants) {
-                 $this->compiler->trigger_template_error("Security: access to constants not permitted");
+            if (isset($this->smarty->security_policy)) {
+                $this->smarty->security_policy->isTrustedConstant(i, $this->compiler);
             }
             res = $this->compiler->compileTag('private_print_expression',a,array('value'=>i, 'modifierlist'=>l));
         } else {
@@ -656,8 +656,8 @@ attributes(res)  ::= . {
                   // attribute
 attribute(res)   ::= SPACE ID(v) EQUAL ID(id). {
     if (defined(id)) {
-        if (isset($this->smarty->security_policy) && !$this->smarty->security_policy->allow_constants) {
-             $this->compiler->trigger_template_error("Security: access to constants not permitted");
+        if (isset($this->smarty->security_policy)) {
+            $this->smarty->security_policy->isTrustedConstant(id, $this->compiler);
         }
         res = array(v=>id);
     } else {
@@ -880,8 +880,8 @@ value(res)       ::= DOT INTEGER(n1). {
                  // ID, true, false, null
 value(res)       ::= ID(id). {
     if (defined(id)) {
-        if (isset($this->smarty->security_policy) && !$this->smarty->security_policy->allow_constants) {
-             $this->compiler->trigger_template_error("Security: access to constants not permitted");
+        if (isset($this->smarty->security_policy)) {
+             $this->smarty->security_policy->isTrustedConstant(id, $this->compiler);
         }
         res = id;
     } else {
@@ -1040,9 +1040,9 @@ indexdef(res)    ::= DOT DOLLAR varvar(v) AT ID(p). {
 
 indexdef(res)   ::= DOT ID(i). {
     if (defined(i)) {
-        if (isset($this->smarty->security_policy) && !$this->smarty->security_policy->allow_constants) {
-             $this->compiler->trigger_template_error("Security: access to constants not permitted");
-        }
+            if (isset($this->smarty->security_policy)) {
+                $this->smarty->security_policy->isTrustedConstant(i, $this->compiler);
+            }
             res = "[". i ."]";
         } else {
             res = "['". i ."']";
diff --git a/libs/sysplugins/smarty_internal_templateparser.php b/libs/sysplugins/smarty_internal_templateparser.php
index bb8e1985..783a81a9 100644
--- a/libs/sysplugins/smarty_internal_templateparser.php
+++ b/libs/sysplugins/smarty_internal_templateparser.php
@@ -2549,8 +2549,8 @@ class Smarty_Internal_Templateparser
     function yy_r32()
     {
         if (defined($this->yystack[$this->yyidx + - 1]->minor)) {
-            if (isset($this->smarty->security_policy) && !$this->smarty->security_policy->allow_constants) {
-                $this->compiler->trigger_template_error("Security: access to constants not permitted");
+            if (isset($this->smarty->security_policy)) {
+                $this->smarty->security_policy->isTrustedConstant($this->yystack[$this->yyidx + - 1]->minor, $this->compiler);
             }
             $this->_retvalue = $this->compiler->compileTag('private_print_expression', $this->yystack[$this->yyidx + 0]->minor, array('value' => $this->yystack[$this->yyidx + - 1]->minor));
         } else {
@@ -2562,8 +2562,8 @@ class Smarty_Internal_Templateparser
     function yy_r33()
     {
         if (defined($this->yystack[$this->yyidx + 0]->minor)) {
-            if (isset($this->smarty->security_policy) && !$this->smarty->security_policy->allow_constants) {
-                $this->compiler->trigger_template_error("Security: access to constants not permitted");
+            if (isset($this->smarty->security_policy)) {
+                $this->smarty->security_policy->isTrustedConstant($this->yystack[$this->yyidx + 0]->minor, $this->compiler);
             }
             $this->_retvalue = $this->compiler->compileTag('private_print_expression', array(), array('value' => $this->yystack[$this->yyidx + 0]->minor));
         } else {
@@ -2575,8 +2575,8 @@ class Smarty_Internal_Templateparser
     function yy_r34()
     {
         if (defined($this->yystack[$this->yyidx + - 2]->minor)) {
-            if (isset($this->smarty->security_policy) && !$this->smarty->security_policy->allow_constants) {
-                $this->compiler->trigger_template_error("Security: access to constants not permitted");
+            if (isset($this->smarty->security_policy)) {
+                $this->smarty->security_policy->isTrustedConstant($this->yystack[$this->yyidx + - 2]->minor, $this->compiler);
             }
             $this->_retvalue = $this->compiler->compileTag('private_print_expression', $this->yystack[$this->yyidx + 0]->minor, array('value' => $this->yystack[$this->yyidx + - 2]->minor, 'modifierlist' => $this->yystack[$this->yyidx + - 1]->minor));
         } else {
@@ -2733,8 +2733,8 @@ class Smarty_Internal_Templateparser
     function yy_r61()
     {
         if (defined($this->yystack[$this->yyidx + 0]->minor)) {
-            if (isset($this->smarty->security_policy) && !$this->smarty->security_policy->allow_constants) {
-                $this->compiler->trigger_template_error("Security: access to constants not permitted");
+            if (isset($this->smarty->security_policy)) {
+                $this->smarty->security_policy->isTrustedConstant($this->yystack[$this->yyidx + 0]->minor, $this->compiler);
             }
             $this->_retvalue = array($this->yystack[$this->yyidx + - 2]->minor => $this->yystack[$this->yyidx + 0]->minor);
         } else {
@@ -2891,8 +2891,8 @@ class Smarty_Internal_Templateparser
     function yy_r108()
     {
         if (defined($this->yystack[$this->yyidx + 0]->minor)) {
-            if (isset($this->smarty->security_policy) && !$this->smarty->security_policy->allow_constants) {
-                $this->compiler->trigger_template_error("Security: access to constants not permitted");
+            if (isset($this->smarty->security_policy)) {
+                $this->smarty->security_policy->isTrustedConstant($this->yystack[$this->yyidx + 0]->minor, $this->compiler);
             }
             $this->_retvalue = $this->yystack[$this->yyidx + 0]->minor;
         } else {
@@ -3012,8 +3012,8 @@ class Smarty_Internal_Templateparser
     function yy_r133()
     {
         if (defined($this->yystack[$this->yyidx + 0]->minor)) {
-            if (isset($this->smarty->security_policy) && !$this->smarty->security_policy->allow_constants) {
-                $this->compiler->trigger_template_error("Security: access to constants not permitted");
+            if (isset($this->smarty->security_policy)) {
+                $this->smarty->security_policy->isTrustedConstant($this->yystack[$this->yyidx + 0]->minor, $this->compiler);
             }
             $this->_retvalue = "[" . $this->yystack[$this->yyidx + 0]->minor . "]";
         } else {
diff --git a/libs/sysplugins/smarty_security.php b/libs/sysplugins/smarty_security.php
index 64354f90..5a70c618 100644
--- a/libs/sysplugins/smarty_security.php
+++ b/libs/sysplugins/smarty_security.php
@@ -54,6 +54,12 @@ class Smarty_Security
      * @var array
      */
     public $trusted_uri = array();
+    /**
+     * List of trusted constants names
+     *
+     * @var array
+     */
+    public $trusted_constants = array();
     /**
      * This is an array of trusted static classes.
      * If empty access to all static classes is allowed.
@@ -410,6 +416,33 @@ class Smarty_Security
         return false; // should not, but who knows what happens to the compiler in the future?
     }
 
+    /**
+     * Check if constants are enabled or trusted
+     *
+     * @param  string $const    contant name
+     * @param  object $compiler compiler object
+     *
+     * @return bool
+     */
+    public function isTrustedConstant($const, $compiler)
+    {
+        if (in_array($const, array('true', 'false', 'null'))) {
+            return true;
+        }
+        if (!empty($this->trusted_constants)) {
+            if (!in_array($const, $this->trusted_constants)) {
+                $compiler->trigger_template_error("Security: access to constant '{$const}' not permitted");
+                return false;
+            }
+            return true;
+        }
+        if ($this->allow_constants) {
+            return true;
+        }
+        $compiler->trigger_template_error("Security: access to constants not permitted");
+        return false;
+    }
+
     /**
      * Check if stream is trusted.
      *