diff --git a/ostd/string.hh b/ostd/string.hh
index e57ca2a..657561c 100644
--- a/ostd/string.hh
+++ b/ostd/string.hh
@@ -790,7 +790,7 @@ namespace utf {
     bool decode(wstring_range &r, char32_t &ret) noexcept;
 
     template<typename R, typename C>
-    bool decode(R &sink, basic_char_range<C const> &r) {
+    inline bool decode(R &sink, basic_char_range<C const> &r) {
         if (char32_t ch; utf::decode(r, ch)) {
             sink.put(ch);
             return true;