diff --git a/src/Compiler/Template.php b/src/Compiler/Template.php
index 03ee51102..e584236a0 100644
--- a/src/Compiler/Template.php
+++ b/src/Compiler/Template.php
@@ -464,7 +464,7 @@ public function compileTemplateSource(\Smarty\Template $template, \Smarty\Compil
 	public function compileTag($tag, $args, $parameter = []) {
 		$this->prefixCodeStack[] = $this->prefix_code;
 		$this->prefix_code = [];
-		$result = $this->compileTag2(strtolower($tag), $args, $parameter);
+		$result = $this->compileTag2($tag, $args, $parameter);
 		$this->prefix_code = array_merge($this->prefix_code, array_pop($this->prefixCodeStack));
 		return $result;
 	}
@@ -591,6 +591,7 @@ public function processText($text) {
 	 * @return ?\Smarty\Compile\CompilerInterface tag compiler object or null if not found or untrusted by security policy
 	 */
 	public function getTagCompiler($tag): ?\Smarty\Compile\CompilerInterface {
+        $tag = strtolower($tag);
 
 		if (isset($this->smarty->security_policy) && !$this->smarty->security_policy->isTrustedTag($tag, $this)) {
 			return null;
@@ -1114,7 +1115,7 @@ private function compileTag2($tag, $args, $parameter) {
 			}
 		}
 
-		// call to function previousely defined by {function} tag
+		// call to function previously defined by {function} tag
 		if ($this->canCompileTemplateFunctionCall($tag)) {
 
 			if (!empty($parameter['modifierlist'])) {
diff --git a/src/Security.php b/src/Security.php
index 46cddcee6..2f654d4ea 100644
--- a/src/Security.php
+++ b/src/Security.php
@@ -261,6 +261,8 @@ public function isTrustedStaticClassAccess($class_name, $params, $compiler) {
 	 * @return boolean                 true if tag is trusted
 	 */
 	public function isTrustedTag($tag_name, $compiler) {
+        $tag_name = strtolower($tag_name);
+
 		// check for internal always required tags
 		if (in_array($tag_name,	['assign', 'call'])) {
 			return true;
diff --git a/tests/UnitTests/SmartyMethodsTests/RegisterFunction/RegisterFunctionTest.php b/tests/UnitTests/SmartyMethodsTests/RegisterFunction/RegisterFunctionTest.php
index 6aa912407..7c7385059 100644
--- a/tests/UnitTests/SmartyMethodsTests/RegisterFunction/RegisterFunctionTest.php
+++ b/tests/UnitTests/SmartyMethodsTests/RegisterFunction/RegisterFunctionTest.php
@@ -39,6 +39,17 @@ public function testRegisterFunction()
         $this->assertEquals('hello world 1', $this->smarty->fetch('eval:{testfunction value=1}'));
     }
 
+    /**
+     * test registerPlugin method for function case-sensitive
+     */
+    public function testRegisterFunctionCaseInsensitive()
+    {
+        $this->smarty->registerPlugin(Smarty::PLUGIN_FUNCTION, 'testFunction', 'myfunction');
+        $this->assertEquals('myfunction',
+            $this->smarty->getRegisteredPlugin(Smarty::PLUGIN_FUNCTION, 'testFunction')[0]);
+        $this->assertEquals('hello world 1', $this->smarty->fetch('eval:{testFunction value=1}'));
+    }
+
     /**
      * test registerPlugin method for function  class
      */