diff --git a/include/simstr/sstring.h b/include/simstr/sstring.h
index e63ad90..e51a529 100644
--- a/include/simstr/sstring.h
+++ b/include/simstr/sstring.h
@@ -322,7 +322,7 @@ struct int_convert { // NOLINT
             if constexpr (sizeof(K) == 1) {
                 return NUMBERS[us];
             } else {
-                return us < 256 ? NUMBERS[us] : 255;
+                return us < 256 ? NUMBERS[us] : us;
             }
         }
     }
diff --git a/src/sstring.cpp b/src/sstring.cpp
index feff50a..52d4b7c 100644
--- a/src/sstring.cpp
+++ b/src/sstring.cpp
@@ -1463,9 +1463,9 @@ SIMSTR_API std::optional<double> impl_to_double(const K* start, const K* end) {
     return d;
 }
 
-template std::optional<double> impl_to_double<u8s>(const u8s* start, const u8s* end);
-template std::optional<double> impl_to_double<u16s>(const u16s* start, const u16s* end);
-template std::optional<double> impl_to_double<u32s>(const u32s* start, const u32s* end);
-template std::optional<double> impl_to_double<uws>(const uws* start, const uws* end);
+template SIMSTR_API std::optional<double> impl_to_double<u8s>(const u8s* start, const u8s* end);
+template SIMSTR_API std::optional<double> impl_to_double<u16s>(const u16s* start, const u16s* end);
+template SIMSTR_API std::optional<double> impl_to_double<u32s>(const u32s* start, const u32s* end);
+template SIMSTR_API std::optional<double> impl_to_double<uws>(const uws* start, const uws* end);
 
 } // namespace simstr