diff --git a/core/string/ustring.cpp b/core/string/ustring.cpp
index e73b02c3a..af0688d94 100644
--- a/core/string/ustring.cpp
+++ b/core/string/ustring.cpp
@@ -4669,15 +4669,66 @@ String String::property_name_encode() const {
 }
 
 // Changes made to the set of invalid characters must also be reflected in the String documentation.
-const String String::invalid_node_name_characters = ". : @ / \" %";
+
+static const char32_t invalid_node_name_characters[] = { '.', ':', '@', '/', '\"', '%', 0 };
+
+String String::get_invalid_node_name_characters() {
+	// Do not use this function for critical validation.
+	String r;
+	const char32_t *c = invalid_node_name_characters;
+	while (*c) {
+		if (c != invalid_node_name_characters) {
+			r += " ";
+		}
+		r += String::chr(*c);
+		c++;
+	}
+	return r;
+}
 
 String String::validate_node_name() const {
-	Vector<String> chars = String::invalid_node_name_characters.split(" ");
-	String name = this->replace(chars[0], "");
-	for (int i = 1; i < chars.size(); i++) {
-		name = name.replace(chars[i], "");
+	// This is a critical validation in node addition, so it must be optimized.
+	const char32_t *cn = ptr();
+	if (cn == nullptr) {
+		return String();
 	}
-	return name;
+
+	bool valid = true;
+	uint32_t idx = 0;
+	while (cn[idx]) {
+		const char32_t *c = invalid_node_name_characters;
+		while (*c) {
+			if (cn[idx] == *c) {
+				valid = false;
+				break;
+			}
+			c++;
+		}
+		if (!valid) {
+			break;
+		}
+		idx++;
+	}
+
+	if (valid) {
+		return *this;
+	}
+
+	String validated = *this;
+	char32_t *nn = validated.ptrw();
+	while (nn[idx]) {
+		const char32_t *c = invalid_node_name_characters;
+		while (*c) {
+			if (nn[idx] == *c) {
+				nn[idx] = '_';
+				break;
+			}
+			c++;
+		}
+		idx++;
+	}
+
+	return validated;
 }
 
 static _FORCE_INLINE_ bool _is_valid_identifier_bit(int p_index, char32_t p_char) {
@@ -5604,6 +5655,23 @@ double String::to_double(const CharType *p_str, const CharType **r_end) {
 	return built_in_strtod<CharType>(p_str, (CharType **)r_end);
 }
 
+uint32_t String::num_characters(int64_t p_int) {
+	int r = 1;
+	if (p_int < 0) {
+		r += 1;
+		if (p_int == INT64_MIN) {
+			p_int = INT64_MAX;
+		} else {
+			p_int = -p_int;
+		}
+	}
+	while (p_int >= 10) {
+		p_int /= 10;
+		r++;
+	}
+	return r;
+}
+
 bool String::_base_is_subsequence_of(const String &p_string, bool case_insensitive) const {
 	int len = length();
 	if (len == 0) {
diff --git a/core/string/ustring.h b/core/string/ustring.h
index 2424ddb35..7dca8f0ce 100644
--- a/core/string/ustring.h
+++ b/core/string/ustring.h
@@ -387,6 +387,8 @@ public:
 	static double to_double(const wchar_t *p_str, const wchar_t **r_end = nullptr);
 	static double to_double(const CharType *p_str, const CharType **r_end = nullptr);
 
+	static uint32_t num_characters(int64_t p_int);
+
 	String capitalize() const;
 	String camelcase_to_underscore(bool lowercase = true) const;
 
@@ -500,7 +502,7 @@ public:
 	String property_name_encode() const;
 
 	// node functions
-	static const String invalid_node_name_characters;
+	static String get_invalid_node_name_characters();
 	String validate_node_name() const;
 	String validate_identifier() const;
 
diff --git a/editor/scene_tree_editor.cpp b/editor/scene_tree_editor.cpp
index 88488b272..4c974f08b 100644
--- a/editor/scene_tree_editor.cpp
+++ b/editor/scene_tree_editor.cpp
@@ -856,7 +856,7 @@ void SceneTreeEditor::_renamed() {
 	String raw_new_name = which->get_text(0);
 	String new_name = raw_new_name.validate_node_name();
 	if (new_name != raw_new_name) {
-		error->set_text(TTR("Invalid node name, the following characters are not allowed:") + "\n" + String::invalid_node_name_characters);
+		error->set_text(TTR("Invalid node name, the following characters are not allowed:") + "\n" + String::get_invalid_node_name_characters());
 		error->popup_centered_minsize();
 
 		if (new_name.empty()) {
diff --git a/scene/main/node.cpp b/scene/main/node.cpp
index 8a72057e3..249b1e235 100644
--- a/scene/main/node.cpp
+++ b/scene/main/node.cpp
@@ -1346,8 +1346,31 @@ void Node::_validate_child_name(Node *p_child, bool p_force_human_readable) {
 
 		if (!unique) {
 			ERR_FAIL_COND(!node_hrcr_count.ref());
-			String name = "@" + String(p_child->get_name()) + "@" + itos(node_hrcr_count.get());
-			p_child->data.name = name;
+
+			// Optimized version of the code below:
+			// String name = "@" + String(p_child->get_name()) + "@" + itos(node_hrcr_count.get());
+			uint32_t c = node_hrcr_count.get();
+			String cn = p_child->get_class_name().operator String();
+			const char32_t *cn_ptr = cn.ptr();
+			uint32_t cn_length = cn.length();
+			uint32_t c_chars = String::num_characters(c);
+			uint32_t len = 2 + cn_length + c_chars;
+			char32_t *str = (char32_t *)alloca(sizeof(char32_t) * (len + 1));
+			uint32_t idx = 0;
+			str[idx++] = '@';
+			for (uint32_t i = 0; i < cn_length; i++) {
+				str[idx++] = cn_ptr[i];
+			}
+			str[idx++] = '@';
+			idx += c_chars;
+			ERR_FAIL_COND(idx != len);
+			str[idx] = 0;
+			while (c) {
+				str[--idx] = '0' + (c % 10);
+				c /= 10;
+			}
+
+			p_child->data.name = String(str);
 		}
 	}
 }