diff --git a/apps/openmw/mwmechanics/npcstats.cpp b/apps/openmw/mwmechanics/npcstats.cpp
index eb2523372..26c4c8e9a 100644
--- a/apps/openmw/mwmechanics/npcstats.cpp
+++ b/apps/openmw/mwmechanics/npcstats.cpp
@@ -220,7 +220,7 @@ void MWMechanics::NpcStats::increaseSkill(int skillIndex, const ESM::Class &clas
     std::stringstream message;
     message << boost::format(MWBase::Environment::get().getWindowManager ()->getGameSettingString ("sNotifyMessage39", ""))
                % std::string("#{" + ESM::Skill::sSkillNameIds[skillIndex] + "}")
-               % base;
+               % static_cast<int> (base);
     MWBase::Environment::get().getWindowManager ()->messageBox(message.str(), std::vector<std::string>());
 
     if (mLevelProgress >= 10)