diff --git a/src/to_string.hpp b/src/to_string.hpp
index 18561bef..f9fb7d9f 100644
--- a/src/to_string.hpp
+++ b/src/to_string.hpp
@@ -29,6 +29,7 @@ namespace str
 {
   std::string to(const bool);
   std::string to(const int);
+  std::string to(const uint32_t);
   std::string to(const uint64_t);
   std::string to(const int64_t);
   std::string to(const std::string&);