diff --git a/source/utf8/checked.h b/source/utf8/checked.h
index 993b7f7..9b0a98d 100644
--- a/source/utf8/checked.h
+++ b/source/utf8/checked.h
@@ -148,7 +148,7 @@ namespace utf8
             case internal::INVALID_LEAD :
             case internal::INCOMPLETE_SEQUENCE :
             case internal::OVERLONG_SEQUENCE :
-                throw invalid_utf8(*it);
+                throw invalid_utf8(static_cast<uint8_t>(*it));
             case internal::INVALID_CODE_POINT :
                 throw invalid_code_point(cp);
         }
diff --git a/source/utf8/cpp11.h b/source/utf8/cpp11.h
index d93961b..2366f12 100644
--- a/source/utf8/cpp11.h
+++ b/source/utf8/cpp11.h
@@ -70,7 +70,7 @@ namespace utf8
     inline std::size_t find_invalid(const std::string& s)
     {
         std::string::const_iterator invalid = find_invalid(s.begin(), s.end());
-        return (invalid == s.end()) ? std::string::npos : (invalid - s.begin());
+        return (invalid == s.end()) ? std::string::npos : static_cast<std::size_t>(invalid - s.begin());
     }
 
     inline bool is_valid(const std::string& s)
diff --git a/source/utf8/cpp17.h b/source/utf8/cpp17.h
index 7bfa869..32a77ce 100644
--- a/source/utf8/cpp17.h
+++ b/source/utf8/cpp17.h
@@ -70,7 +70,7 @@ namespace utf8
     inline std::size_t find_invalid(std::string_view s)
     {
         std::string_view::const_iterator invalid = find_invalid(s.begin(), s.end());
-        return (invalid == s.end()) ? std::string_view::npos : (invalid - s.begin());
+        return (invalid == s.end()) ? std::string_view::npos : static_cast<std::size_t>(invalid - s.begin());
     }
 
     inline bool is_valid(std::string_view s)