diff --git a/include/clara.hpp b/include/clara.hpp
index fddfac6..b072191 100644
--- a/include/clara.hpp
+++ b/include/clara.hpp
@@ -149,7 +149,7 @@ namespace detail {
             return !m_tokenBuffer.empty() || it != itEnd;
         }
 
-        auto count() const -> size_t { return m_tokenBuffer.size() + (itEnd - it); }
+        auto count() const -> size_t { return m_tokenBuffer.size() + static_cast<unsigned long>(itEnd - it); }
 
         auto operator*() const -> Token {
             assert( !m_tokenBuffer.empty() );