diff --git a/include/stringfield.h b/include/stringfield.h
index f9dd7da..85ddef9 100644
--- a/include/stringfield.h
+++ b/include/stringfield.h
@@ -119,7 +119,7 @@ public:
     virtual size_t size() const override
     {
         // find out size of the size parameter
-        T size(_data.size());
+        T size((T::Type)_data.size());
 
         // size of the uint8 or uint32 + the actual string size
         return size.size() + _data.size();
@@ -160,7 +160,7 @@ public:
     virtual void fill(OutBuffer& buffer) const override
     {
         // create size
-        T size(_data.size());
+        T size((T::Type)_data.size());
 
         // first, write down the size of the string
         size.fill(buffer);