diff --git a/include/flecs/addons/cpp/utils/string.hpp b/include/flecs/addons/cpp/utils/string.hpp
index 1f26ba998..1e19d0be9 100644
--- a/include/flecs/addons/cpp/utils/string.hpp
+++ b/include/flecs/addons/cpp/utils/string.hpp
@@ -96,7 +96,7 @@ struct string {
         return m_const_str;
     }
 
-    std::size_t length() {
+    std::size_t length() const {
         return static_cast<std::size_t>(m_length);
     }
 
@@ -105,7 +105,7 @@ struct string {
         return N - 1;
     }
 
-    std::size_t size() {
+    std::size_t size() const {
         return length();
     }