diff --git a/ext/dom/element.c b/ext/dom/element.c
index d3bcad34ed999..6fcaee5888e33 100644
--- a/ext/dom/element.c
+++ b/ext/dom/element.c
@@ -816,7 +816,12 @@ static void dom_element_get_elements_by_tag_name(INTERNAL_FUNCTION_PARAMETERS, b
 	dom_object *intern, *namednode;
 	char *name;
 
-	if (zend_parse_parameters(ZEND_NUM_ARGS(), "s", &name, &name_len) == FAILURE) {
+	if (zend_parse_parameters(ZEND_NUM_ARGS(), "p", &name, &name_len) == FAILURE) {
+		RETURN_THROWS();
+	}
+
+	if (name_len > INT_MAX) {
+		zend_argument_value_error(1, "is too long");
 		RETURN_THROWS();
 	}
 
@@ -1239,7 +1244,17 @@ static void dom_element_get_elements_by_tag_name_ns(INTERNAL_FUNCTION_PARAMETERS
 	dom_object *intern, *namednode;
 	char *uri, *name;
 
-	if (zend_parse_parameters(ZEND_NUM_ARGS(), "s!s", &uri, &uri_len, &name, &name_len) == FAILURE) {
+	if (zend_parse_parameters(ZEND_NUM_ARGS(), "p!p", &uri, &uri_len, &name, &name_len) == FAILURE) {
+		RETURN_THROWS();
+	}
+
+	if (uri_len > INT_MAX) {
+		zend_argument_value_error(1, "is too long");
+		RETURN_THROWS();
+	}
+
+	if (name_len > INT_MAX) {
+		zend_argument_value_error(2, "is too long");
 		RETURN_THROWS();
 	}
 
diff --git a/ext/dom/php_dom.c b/ext/dom/php_dom.c
index 939c179452086..9c3922ab5f625 100644
--- a/ext/dom/php_dom.c
+++ b/ext/dom/php_dom.c
@@ -1473,7 +1473,7 @@ void dom_namednode_iter(dom_object *basenode, int ntype, dom_object *intern, xml
 	const xmlChar* tmp;
 
 	if (local) {
-		int len = local_len > INT_MAX ? -1 : (int) local_len;
+		int len = (int) local_len;
 		if (doc != NULL && (tmp = xmlDictExists(doc->dict, (const xmlChar *)local, len)) != NULL) {
 			mapptr->local = BAD_CAST tmp;
 		} else {
@@ -1481,15 +1481,11 @@ void dom_namednode_iter(dom_object *basenode, int ntype, dom_object *intern, xml
 			mapptr->free_local = true;
 		}
 		mapptr->local_lower = BAD_CAST estrdup(local);
-		if (len < 0) {
-			zend_str_tolower((char *) mapptr->local_lower, strlen((const char *) mapptr->local_lower));
-		} else {
-			zend_str_tolower((char *) mapptr->local_lower, len);
-		}
+		zend_str_tolower((char *) mapptr->local_lower, len);
 	}
 
 	if (ns) {
-		int len = ns_len > INT_MAX ? -1 : (int) ns_len;
+		int len = (int) ns_len;
 		if (doc != NULL && (tmp = xmlDictExists(doc->dict, (const xmlChar *)ns, len)) != NULL) {
 			mapptr->ns = BAD_CAST tmp;
 		} else {
diff --git a/ext/dom/tests/gh16465.phpt b/ext/dom/tests/gh16465.phpt
new file mode 100644
index 0000000000000..b09f5de7dcc3c
--- /dev/null
+++ b/ext/dom/tests/gh16465.phpt
@@ -0,0 +1,29 @@
+--TEST--
+GH-16465 (Heap buffer overflow in DOMNode->getElementByTagName)
+--EXTENSIONS--
+dom
+--FILE--
+<?php
+
+$v10 = new DOMElement("a");
+try {
+    $v10->getElementsByTagName("text\0something");
+} catch (ValueError $e) {
+    echo $e->getMessage(), "\n";
+}
+try {
+    $v10->getElementsByTagNameNS("", "text\0something");
+} catch (ValueError $e) {
+    echo $e->getMessage(), "\n";
+}
+try {
+    $v10->getElementsByTagNameNS("text\0something", "");
+} catch (ValueError $e) {
+    echo $e->getMessage(), "\n";
+}
+
+?>
+--EXPECT--
+DOMElement::getElementsByTagName(): Argument #1 ($qualifiedName) must not contain any null bytes
+DOMElement::getElementsByTagNameNS(): Argument #2 ($localName) must not contain any null bytes
+DOMElement::getElementsByTagNameNS(): Argument #1 ($namespace) must not contain any null bytes