diff --git a/core/extension/gdextension_interface.cpp b/core/extension/gdextension_interface.cpp
index 011c96a66d2..d591fc62b25 100644
--- a/core/extension/gdextension_interface.cpp
+++ b/core/extension/gdextension_interface.cpp
@@ -902,8 +902,9 @@ static void gdextension_string_new_with_wide_chars(GDExtensionUninitializedStrin
 }
 
 static void gdextension_string_new_with_latin1_chars_and_len(GDExtensionUninitializedStringPtr r_dest, const char *p_contents, GDExtensionInt p_size) {
+	const size_t string_length = p_contents ? (p_size < 0 ? strlen(p_contents) : strnlen(p_contents, p_size)) : 0;
 	String *dest = memnew_placement(r_dest, String);
-	dest->append_latin1(Span(p_contents, p_contents ? _strlen_clipped(p_contents, p_size) : 0));
+	dest->append_latin1(Span(p_contents, string_length));
 }
 
 static void gdextension_string_new_with_utf8_chars_and_len(GDExtensionUninitializedStringPtr r_dest, const char *p_contents, GDExtensionInt p_size) {
@@ -927,8 +928,9 @@ static GDExtensionInt gdextension_string_new_with_utf16_chars_and_len2(GDExtensi
 }
 
 static void gdextension_string_new_with_utf32_chars_and_len(GDExtensionUninitializedStringPtr r_dest, const char32_t *p_contents, GDExtensionInt p_char_count) {
+	const size_t string_length = p_contents ? (p_char_count < 0 ? strlen(p_contents) : strnlen(p_contents, p_char_count)) : 0;
 	String *string = memnew_placement(r_dest, String);
-	string->append_utf32(Span(p_contents, p_contents ? _strlen_clipped(p_contents, p_char_count) : 0));
+	string->append_utf32(Span(p_contents, string_length));
 }
 
 static void gdextension_string_new_with_wide_chars_and_len(GDExtensionUninitializedStringPtr r_dest, const wchar_t *p_contents, GDExtensionInt p_char_count) {
@@ -938,8 +940,9 @@ static void gdextension_string_new_with_wide_chars_and_len(GDExtensionUninitiali
 		dest->append_utf16((const char16_t *)p_contents, p_char_count);
 	} else {
 		// wchar_t is 32 bit (UTF-32).
+		const size_t string_length = p_contents ? (p_char_count < 0 ? strlen(p_contents) : strnlen((const char32_t *)p_contents, p_char_count)) : 0;
 		String *string = memnew_placement(r_dest, String);
-		string->append_utf32(Span((const char32_t *)p_contents, p_contents ? _strlen_clipped((const char32_t *)p_contents, p_char_count) : 0));
+		string->append_utf32(Span((const char32_t *)p_contents, string_length));
 	}
 }
 
diff --git a/core/string/ustring.h b/core/string/ustring.h
index 2a006de8d17..fc153a52e75 100644
--- a/core/string/ustring.h
+++ b/core/string/ustring.h
@@ -66,41 +66,47 @@ constexpr size_t strlen(const char32_t *p_str) {
 }
 
 // strlen equivalent function for wchar_t * arguments; depends on the platform.
-constexpr size_t strlen(const wchar_t *str) {
+constexpr size_t strlen(const wchar_t *p_str) {
 	// Use static_cast twice because reinterpret_cast is not allowed in constexpr
 #ifdef WINDOWS_ENABLED
 	// wchar_t is 16-bit
-	return strlen(static_cast<const char16_t *>(static_cast<const void *>(str)));
+	return strlen(static_cast<const char16_t *>(static_cast<const void *>(p_str)));
 #else
 	// wchar_t is 32-bit
-	return strlen(static_cast<const char32_t *>(static_cast<const void *>(str)));
+	return strlen(static_cast<const char32_t *>(static_cast<const void *>(p_str)));
 #endif
 }
 
-constexpr size_t _strlen_clipped(const char *p_str, int p_clip_to_len) {
-	if (p_clip_to_len < 0) {
-		return strlen(p_str);
-	}
-
-	int len = 0;
+// strnlen equivalent function for char16_t * arguments.
+constexpr size_t strnlen(const char16_t *p_str, size_t p_clip_to_len) {
+	size_t len = 0;
 	while (len < p_clip_to_len && *(p_str++) != 0) {
 		len++;
 	}
 	return len;
 }
 
-constexpr size_t _strlen_clipped(const char32_t *p_str, int p_clip_to_len) {
-	if (p_clip_to_len < 0) {
-		return strlen(p_str);
-	}
-
-	int len = 0;
+// strnlen equivalent function for char32_t * arguments.
+constexpr size_t strnlen(const char32_t *p_str, size_t p_clip_to_len) {
+	size_t len = 0;
 	while (len < p_clip_to_len && *(p_str++) != 0) {
 		len++;
 	}
 	return len;
 }
 
+// strnlen equivalent function for wchar_t * arguments; depends on the platform.
+constexpr size_t strnlen(const wchar_t *p_str, size_t p_clip_to_len) {
+	// Use static_cast twice because reinterpret_cast is not allowed in constexpr
+#ifdef WINDOWS_ENABLED
+	// wchar_t is 16-bit
+	return strnlen(static_cast<const char16_t *>(static_cast<const void *>(p_str)), p_clip_to_len);
+#else
+	// wchar_t is 32-bit
+	return strnlen(static_cast<const char32_t *>(static_cast<const void *>(p_str)), p_clip_to_len);
+#endif
+}
+
 template <typename L, typename R>
 constexpr int64_t str_compare(const L *l_ptr, const R *r_ptr) {
 	while (true) {